The Red Devils' impressive form has seen them open up a five-point advantage at the summit, with 13 games of the campaign remaining.
And Dutch goalkeeper Van der Sar, who has recorded 14 straight clean sheets, is focused on United's own quest rather than distracting himself with their rivals' pursuits.
"Footballers have to be strong," he said. "Seeing their rivals win won't stop their determination.
"That is why we think of ourselves and what we can do to win games and stay top of the league.
"That way, when it comes to the finishing line, hopefully we will have our noses in front of Chelsea and Liverpool, who are now our main rivals for the title."