Kylian Mbappe marked his return from injury with a goal as Paris St-Germain took control of their Champions League last-16 tie against Real Sociedad.
The French champions have an underwhelming record in the competition and were enduring a frustrating night until Mbappe pounced.
Having missed his side's previous match with an ankle problem, Mbappe scored at the back post after a corner.
Bradley Barcola added the second with a lovely finish past Alex Remiro.
Real Sociedad keeper Remiro had earlier denied Mbappe a second when he tipped his attempt on to the crossbar.
PSG, who have never won the Champions League, were far from their best in the first half and Real Sociedad's Mikel Merino hit the bar just before half-time.
"If you told me at half-time we would win 2-0, I would be dancing for two hours," PSG manager Luis Enrique told TNT Sports.
"We had to change everything because they were pressing us very high. We couldn't press and it was like a nightmare.
"When that happens you are going to lose confidence, but football is unbelievable and we could change that. In the second half it was more what we wanted."
Real Sociedad will believe they can turn it around in the second leg in Spain on 5 March, but will have to offer a much more attacking threat than in Paris.