Paris Saint-Germain head coach Luis Enrique on Wednesday paid tribute to his side's mental strength after they overturned a two-goal deficit against Monaco to win 3-2 at the Stade Louis II.
Folarin Balogun scored twice within the first 20 minutes and PSG midfielder Vitinha missed a penalty to compound the visitors' woes.
However, Désiré Doué, a substitute for the injured Ousmane Dembélé, pulled one back after 29 minutes.
Morocco international skipper Achraf Hakimi levelled just before half-time.
Doué scored his second of the match mid way through the second period to cap the comeback against Monaco who had been reduced to 10 men following the dismissal of midfielder Aleksandr Golovin just after the restart.
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"Normally, when a team starts a match like that, the most likely outcome is a loss,” said Enrique.
“It was catastrophic. The first two times they overcame our pressure and entered our half, they scored. They made some very good plays.
“After that, it's difficult to have confidence but we showed our mental strength.
"In the last six times we've played here in Monaco, this is only the second time we've won, which shows how difficult it is.”
Sébastien Pocognoli, Enrique's Monaco counterpart, also paid tribute to his squad despite the defeat.
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"I told my players that they had given their all in the second-half, playing 10 against 11 and that I didn't want them to have any negative thoughts.
"There is a return leg to come next week and we've put ourselves in a position where there's still something to play for."
In other first leg games in the play-offs for a place in the last-16, Real Madrid's 1-0 win at Benfica was overshadowed by allegations of racism.
Madrid striker Vincius Junior claimed that after scoring Madrid's goal at the Estádio da Luz, Benfica's Gianluca Prestianni made racist comments to him while covering his mouth with his shirt.
Vinícius immediately ran to the referee, François Letexier, who stopped the match and crossed his arms to signal that he was activating the anti-racism protocol.
European football's governing body Uefa, which organises the competition, said it will investigate the incident.
Elsewhere, Galatasaray walloped Juventus 5-2 and Borussia Dortmund saw off Atalanta 2-0.
