Second-half substitute Blaise Matuidi struck with just over a minute of normal time remaining as Paris Saint-Germain moved to within one win of securing the Ligue 1 title with victory over 10-man Evian TG.
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Wass then went close again when his header was saved by Sirigu.
The match swung heavily in PSG's favour when Evian right-back Kassim Abdallah picked up two bookings in eight minutes to be sent off.
Laurent Blanc's side kept knocking at the door and eventually they found a way through when Matuidi fired low across goal into the bottom corner.
Three points puts PSG 10 points clear of second-placed Monaco with four games of the season remaining. Evian remain five clear of the drop zone.