Kylian Mbappe scored the opener as Paris Saint-Germain took a big step towards reaching the Champions League quarterfinals with a 2-0 win over Real Sociedad in the first leg of their last-16 tie on Wednesday.

The mediocrity of PSG's first-half performance at the Parc des Princes may have had their supporters fearing another in a long line of disappointing results down the years in the Champions League knockout stages.

But Mbappe, who is expected to leave the club at the end of the season when his contract expires, broke the deadlock from close range just before the hour mark.

Bradley Barcola's well-taken goal in the 70th minute then made it 2-0 to give the French champions a comfortable cushion to take to Spain for the return early next month.

"We managed to score at key moments. We are happy with this first step. There is still a lot of work to do but it is good to be going there with the advantage," Mbappe told broadcasterCanal Plus.

Captain Marquinhos added: "We were in great difficulty in the first half but we knew that would be the case.

"The coach gave us an earbashing at half-time and I think that helped because the attitude was much better in the second half.

"We know how important it is to win at home but it is not finished. We need to keep the same mindset between now and then, keep playing well in the league and then go there and play well to secure our qualification."

There was big pressure on PSG coming into this tie after they had gone out in the last 16 of the Champions League in five of the last seven seasons.

Another early exit from the competition this season would be a monumental setback for the Qatar-owned club, especially as Real Sociedad were appearing in their first Champions League knockout tie in two decades.

They also made the trip to Paris having failed to score a goal while failing to win any of their last four games in all competitions.

In addition to that, they were missing captain and top scorer Mikel Oyarzabal as he recovers from injury.

PSG, who gave a Champions League bow at left-back to 20-year-old Brazilian January signing Lucas Beraldo, were aiming to extend a run of 16 games unbeaten in all competitions stretching back to early November.

AWAY SIDE THREATEN

However, an early shot by Mbappe that was beaten away by visiting goalkeeper Alex Remiro was really the only time they threatened in a poor first-half showing.

Instead it was the away side, winners of their group ahead of Inter Milan, who looked more comfortable and who came closest to scoring prior to the break.

In the final minute of the half, captain Mikel Merino controlled the ball before crashing a piledriver from 25 metres off the top of the bar and over.

PSG eventually broke the deadlock on 58 minutes as Ousmane Dembele's corner from the right was helped on by Marquinhos towards the back post where Mbappe turned it in.

It was a 31st goal of the campaign in all competitions, and a fourth in the Champions League, for the France captain who is widely tipped to move to Real Madrid after this season.

That relaxed the home side and Mbappe almost scored again in the 63rd minute as he won the ball back high up the pitch and hit a powerful shot from outside the box which was tipped onto the bar and over by Remiro.

Luis Enrique's side did find the net again 20 minutes from the end when Barcola collected a ball on the left, skipped away from Hamari Traore on his way into box and then slotted the ball past Remiro for his first ever Champions League goal.

La Real could not find a way back into the game as their run without a goal stretched to five matches.

They now have something of a mountain to climb when they entertain PSG in San Sebastian on 5 March, although supporters of the French side will remain wary given the way they have collapsed at this stage of the competition in recent years against Barcelona and Madrid, among others. (AFP)