Graeme Murty praised supporters on a freezing night as his side beat Sporting and now turns focus to Dortmund.

Graeme Murty praised Sunderland’s supporters for turning out on a bitterly cold Wearside night as his Under-21s beat Sporting CP 1-0 to move top of Group D in the Premier League International Cup – before warning his young players that they will need to “earn” the right to progress when Borussia Dortmund visit in January.

Murty was pleased with much of his side’s display against the Portuguese outfit, highlighted by Romaine Mundle’s match-winning strike on his return from injury, but admitted he wants to see sharper execution in the final third ahead of what he expects to be a far sterner test against Dortmund.

Mundle, making his first start of the season after injury, struck in the 32nd minute at the Stadium of Light after being slipped in by Ben Middlemas. The winger had already threatened twice, and his sharp finish ultimately extended Sunderland’s unbeaten start in Europe this season.

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With several first-team players involved – including Mundle, Leo Hjelde, Dennis Cirkin, Harrison Jones and Blondy Nna Noukeu – Sunderland controlled large spells. Timur Tutierov went close twice, Jake Waters saw a header skim over the bar before half-time, and Middlemas saw a deflected effort drop just wide after the break. Sporting’s best moment came late on when Sandro Ferreira pounced on a loose pass but lashed over.

After the game, Murty paid tribute to the supporters who braved a bitter Wearside night to back the youngsters. “We really appreciate it,” he said. “I think, as we've always said, we try to embrace all the challenges that we have. We love to go and showcase what the players are doing, and the more people we can get in, it's fantastic for the players, and hopefully, they've seen some good bits.

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“We just want to express our gratitude, understanding it's not nice sometimes being a football fan – you get awful weather, it's really cold. Hopefully, we can do a little bit to offset that, but hopefully they want to come back again. If they can tell their mates about it, great, bring a couple more.”

Sunderland host Borussia Dortmund in January – a fixture Murty hopes will draw an even bigger crowd. “I think we've got Borussia Dortmund, is it, in the new year? Hopefully it's a little bit warmer then, but come out and watch, and anyone that comes – we'd be really grateful for them.”

The win takes Sunderland to seven points from three games in Group D, leaving qualification firmly in their hands. Murty, though, was clear that nothing comes easy at this level. “It's something to look forward to, and like we said, we want more opportunities like this,” he said. “The players know they need to perform, because I can't see Dortmund giving anything away.

“We need to go and grasp it and take it and hopefully do enough to progress to the next level, but I'm a really, really big believer that you need to go and earn it. Nothing in this game is given, so if we get to the next round, it's because they'll have done enough to deserve it, and they'll get the rewards for that. Hopefully, having another opportunity to play here. So long may it continue.”

Despite the win, Murty admitted his side’s biggest frustration was their lack of ruthlessness after last week’s more clinical showing. “I think it's not necessarily the outcome that I'm looking at. I'm not looking at scoreline, I'm looking at process, I'm looking at execution,” he said. “I'm looking at the players to understand we're playing against a deeper block, we need to access these areas, we need to pull their shape apart.

“And then when we do get that shape apart, this isn't a regular academy game where, oh well, don't worry about it, we'll get enough opportunity in a minute. They need to understand the closer they get to the first team, it's like the point of a pyramid – you get narrower and narrower and narrower, you get fewer and fewer and fewer opportunities.”

For Murty, the lesson was clear. “You need to demonstrate to the watching fans, to our senior staff, that they can make that step,” he said. “You can do it at 16s level, you can do it at 18s level, you can even do it in PL2 – but the better your opposition becomes, the finer those margins are. And they need to go and demonstrate it. And for me tonight, we didn't show enough of the fine execution at critical moments, and if we had done, I think they would have had an easier night.”

Your next Sunderland read: James Copley's Sunderland U21s player ratings vs Sporting CP – including Mundle, Cirkin and Hjelde grades