When the referee ended the first half, the 12,509 fans at Porto's Estadio do Dragao must have been curious about the Slovenian boy between the sticks for visitors Rio Ave.

The year was 2013, and Jan Oblak had been having himself quite the afternoon in the Taca da Liga semi-final, denying FC Porto with some impressive saves before the teams went into the break level at 0-0.

However, shortly after returning from the dressing room, Oblak undid all his good work. As Porto's midfielder Fernando Reges received a ball unmarked and sent a brilliant pass to forward Jackson Martinez, Oblak left his goal in a desperate attempt to intercept the ball, but instead he took Martinez down inside the box and was immediately sent off. Penalty for the home team.

While Martinez got medical care after the incident, Rio Ave coach Nuno Espirito Santo—now of Wolverhampton Wanderers in the Premier League—rushed substitute Ederson Moraes on to replace Oblak in goal.

The Brazilian teenager with Neymar-esque hair wasn't given much time to warm up and was unable to save the penalty taken by James Rodriguez.

He went on to concede three more as Porto made their man advantage count to secure a place in the final of the competition.

But that's not the reason why that game is still remembered, it is the swap in goal that is so remarkable when looking back on it today.

Off went Jan Oblak—now Atletico Madrid's outstanding stopper and who is on course for his fourth successive Ricardo Zamora Trophy, given to the goalkeeper with the lowest goals-to-games ratio in La Liga.  

On came Ederson—the Brazilian 'keeper who has helped revolutionise the position as a member of Pep Guardiola's electric, Premier League-winning Manchester City side.   

It's astonishing to think that, for one season, a mid-table Portuguese side with a €3.4 million annual budget, from a small town called Vila do Conde, had both Oblak and Ederson, two of the best 'keepers in the world today.

Oblak was 20 years old when he was sent off against Porto, while Ederson was 19 when he came on—it was the only time Rio Ave used the duo in the same match.

TheFootballRepublic @TheFootballRep

Throwback to when Jan Oblak and Ederson were Rio Ave's goalkeepers in 2012/13... 🙌 They helped Rio Ave to their highest top-flight finish in 31 years. 🇵🇹👏

For most of the season, Oblak remained first choice, starting 31 times after arriving on loan from Benfica.

Ederson featured on eight occasions, mostly in the cup matches, and was not as highly rated in the at the time. He had been signed from fourth-tier club Ribeirao and still lacked first-team experience.

Back then, it is hard to imagine any of Vila do Conde's almost 30,000 inhabitants predicting the pair would go on to become world-class goalkeepers so quickly.

Long gone are the days when both of them relied on lifts from their pals to get them to training sessions. Both had to share apartments to save on expenses when they were at Rio Ave, and big-money moves abroad seemed like distant dreams.

When they were both at the club, the average salary for most players was around €5,000 per month.

"When Ederson arrived in Vila do Conde, he struggled to find a place to live and asked to stay with me for a month. We had already known each other from his spell at Ribeirao. It was very difficult to get a house in the summer; most of them were rented and could be a bit more expensive," Marcelo, a former team-mate who now plays for Chicago Fire in MLS, tells Bleacher Report.

The 29-year-old centre-back was not the only one the newly recruited goalkeeper reached out to.

"After that, he decided to share an apartment with Dieguinho [Diego Lopes], whom he must have met at Benfica's academy," Lionn, a right-back currently plying his trade with Chaves in the Portuguese top flight, adds in an interview to B/R.

"I recently invited Dieguinho and his family over for a dinner and we were speaking about Ederson. We used to call him Pato [Duck].

"We were basically saying, 'Look how things are in football, Pato earned perhaps €2,000 to €3,000 per month back then and now is one of the most expensive goalkeepers ever and rides a Ferrari or a Lamborghini to the training ground.'"

At Rio Ave, Ederson didn't even have a driver's license.

"We did driving lessons together in Vila do Conde, he was an amazing guy, always cheerful. We had a private instructor since it wasn't very easy to find much spare time when you are in the middle of the season," Edimar, a left-back now at Sao Paulo, recalls to B/R.

The trio of Lionn, Marcelo and Edimar formed an all-Brazilian back four alongside their compatriot Nivaldo in front of Oblak.

The Slovenian prodigy was in his fourth consecutive loan move after being bought by Benfica at the age of 17 in 2009.

He had always been identified as a strong prospect by the Portuguese giants, who agreed to pay a reported €3.9 million transfer fee for him—making him the most lucrative sale in the history of Olimpija Ljubljana.

Oblak was first sent to minnows Beira-Mar and then to Olhanense and Uniao de Leiria to get more playing time.

Packing his bags once again and moving to Rio Ave in 2012, he was already settled in Portugal and, while far from fluent in the language, was at least able to communicate with his colleagues in some way.

Oblak had a pivotal role in the club's historic sixth-placed campaign, keeping eight clean sheets throughout the season, including in a surprising 1-0 away win at Sporting CP. That campaign, Rio Ave even finished above Sporting in the table for the first time in their history.

"Oblak could understand more than speak Portuguese—he used to hang out more with the English-speaking guys such as Ahmed Hassan [Egyptian forward] and Tope Obadeyi [Nigerian striker]," Lionn says.

Despite that obstacle, he was always around at the group's dinners.

"It is a small city. We all lived close to each other and got together after training. He was more reserved and quiet, but extremely nice every time we tried to chat with him. He must have learned a thing or two about our culture from those nights," Edimar continues.

"We were a gang of 10 Brazilians—almost as large as the Portuguese crew."

Oblak didn't find it difficult adapting to the slow-paced life of Vila do Conde.

"We usually trained in the mornings and then had the afternoons free. I remember Oblak really enjoyed resting up after lunch. He used to say, 'If I have a comfortable sofa and a television, what else do I need?' He was that down to earth and did not need much to be happy," Marcelo recalls.

"I suppose that, in a way, he was aware he wouldn't be around for much longer. Rio Ave was just a step on his way to the top."

Oblak and Ederson benefited from arriving to the team at the same time as Espirito Santo, a reserve goalkeeper for most of his career with Porto and Deportivo La Coruna who was starting his career as a coach.

Back then, Nuno's experience was limited to being an assistant to Jesualdo Ferreira at Malaga and Panathinaikos.

Rio Ave was his first top job, and he wasted no time in revolutionising the club's mentality. He turned the outfit into a new force in the domestic scene who have since made the Europa League group stage once and twice been eliminated in the qualification stages.

Former Real Betis and Benfica forward, Joao Tomas, was with the club for almost four years between 2009 and 2013 and witnessed the transformation of Rio Ave. He was impressed with the changes inside the locker room.

"For me, an era ended and another one started in 2012, with new ideas, more investment on structure, a new coach. I'm not sure if it was clear for those outside, but I can assure it made a huge difference to the team. We realised we had something good going on," Tomas tells B/R.

"When we signed Oblak, it brought me back memories of the game we had lost to his side in the previous season. That kid had been incredible at Leiria."

It's safe to say that apart from opponents, no one had a harder time scoring against Oblak and Ederson than Tomas in training.

However, it seemed to sharpen him, and in three seasons with Rio Ave, the veteran striker netted 53 times in 100 games and was consistently battling the likes of Radamel Falcao, Hulk and Oscar Cardozo at the top of the Portuguese scoring charts.

"We had great duels in the training sessions, pushing each other to the edge—it's the best thing about sharing pitch with colleagues that are so good. They motivate you and drive you to another level. They were spectacular and made the best of their times there," Tomas says.

"In a way, they were very similar in character, always relaxed and having a laugh. Oblak was a bit more distant than Ederson. It's part of his culture: [he] didn't speak much, but was always nice.

"A few months after leaving Rio Ave, I remember doing a radio interview and being asked if I believed Oblak could become Benfica's starting goalkeeper. I told them, 'If he gets a chance, he will not leave the team.' He was clearly above par compared to others.

"I used to joke a lot with Ederson, but we once had a serious conversation, and I told him he needed to work on this thing about his game. If he were a prima donna, he would not have listened to me. But he did and sorted it out."

Besides Oblak and Ederson, Rio Ave also had a couple of other interesting names in their 2012-13 squad, among them Bebe (the Manchester United flop/cult hero) and Liverpool's Fabinho, who had a brief spell, playing just a friendly during pre-season before leaving on loan to Real Madrid).

Those four, and indeed others within the club, had something in common: They were all connected to Portuguese super-agent Jorge Mendes.

Mendes' influence around Vila do Conde is so huge that it's almost impossible to discuss one and not mention the other.

It was particularly massive that season when he secured the coaching position for his first-ever football client, Nuno, and delivered a very promising crop of players—some of them his clients (Ederson, for example) and others from his partners (including Oblak).

Nuno made the most of it, guiding Rio Ave to the finals of the Portuguese League Cup and the Portuguese Cup over his two seasons.

Mendes was the secret behind Oblak and Ederson coinciding in the small coastal town and also the main reason they had to go when their time came.

They were always meant to fly away to better things, but few could have imagined they would both reach so high, so soon.