Pedro Neto’s deflected strike earned a 1-1 draw in the first leg of their Europa League last 16 tie in Athens.
Ruben Semedo was sent off in the first half for the hosts but Youssef El Arabi put them ahead after the break.
Wolves had asked UEFA to postpone the game – an appeal which was rejected – after Olympiacos owner Evangelos Marinakis announced he had tested positive for coronavirus on Tuesday.
The game was already being played behind closed doors at the Karaiskakis Stadium due to the Covid-19 outbreak.
Wolves were confused over why they were forced to play by UEFA and they struggled to overcome a team who played over 60 minutes with 10 men but Nuno insisted it was not because of off-field issues.
He said: “No, let’s be fair to everyone. During the game it was not that feeling. They were focused and organised. Olympiacos are a very good team.
“The game stays with me because I have to work on it and analyse it. It’s very tough, at the beginning of the game it was strange, the energy levels – it was missing someone to push. It was not a very good game.”
Semedo was dismissed during a scrappy first half after he fouled Diogo Jota as the striker threatened to break clear.
But El Arabi opened the scoring nine minutes after the break, tapping in Guilherme’s cross.
Neto levelled 13 minutes later when Joao Moutinho touched on a free-kick and his low effort clipped Andreas Bouchalakis to wrongfoot Jose Sa.
“I tried to help the team to do my best and with 10 guys it was difficult, they closed in behind and now we go to the second game,” Neto told BT Sport.
“I think we could have shot more times but now we focus on the next one.”
Wolves are due to travel to West Ham in the top flight on Sunday, although the Premier League will hold an emergency club meeting on Friday regarding fixtures after Arsenal boss Mikel Arteta tested positive for coronavirus.
“Now we’re going to think about West Ham but we keep on working. Now we have West Ham and hopefully next Thursday we’ll play again,” added Nuno.
“There’s a long way to go, a lot of matches but we’ll go back to the Premier League and we have to rest well, recover. The schedule is very tight.”
Olympiacos boss Pedro Martins did not hold a post-match press conference as the club kept interactions to a minimum.