Surprise defeats for title rivals Marsielle and Lyon had given the champions an opportunity to reclaim top spot with victory at Stade Louis II on Sunday.
But, despite having the better of the chances, Laurent Blanc's side failed to find the breakthrough against Monaco.
Van der Wiel felt his side lacked the necessary poise in the crucial moments but is positive about PSG's chances of retaining the title.
"At this level, you have to kill the matches," Van der Wiel told France Football.
"We had many opportunities, we were solid defensively, we had possession, but this kind of game is played on the details.
"Obviously, we're disappointed because we had the opportunity to take the lead of the championship. But we remain confident, there is still a lot of matches to play before the end of the season."
Blanc will get another chance to get one over on Leonardo Jardim on Wednesday, when the teams meet again at the Parc de Princes in the quarter-final of the Coupe de France.
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