Runaway leaders PSV hammered Twente 5-0 at De Grolsch Veste on Saturday to go 12 points clear at the summit and second-placed Ajax were unable to respond with a victory a day later.
Frank de Boer's men looked set to stretch their winning run to five Eredivisie matches when Leeuwin's own goal put them in front, but substitute Gevero Markiet took advantage of some poor defending to equalise five minutes from time.
Leeuwin's day went from bad to worse when he was shown a straight red card for a challenge on visiting captain Nicolai Boilesen with three minutes remaining, but Ajax were unable to force a winner and PSV now look set for a first title in seven years.
Elvis Manu was on target twice as Feyenoord strengthened their grip on third spot by hammering fourth-placed AZ 4-1 at AFAS Stadion to extend their winning run to four matches.
Feyenoord were gifted the lead when Derrick Luckassen embarrassingly sliced the ball into his own net and goals from Anass Achahbar and Manu put the visitors three goals up at the break.
Manu helped himself to a second goal just before the hour-mark and Sven van Beek's 87th-minute own goal was no consolation for AZ, who are now seven points adrift of Fred Rutten's side.
Max Kramer scored his 15th and 16th goals of the season, one of which was a stoppage-time winner, as Den Haag ended their three-game losing to win 3-2 at Excelsior to leapfrog their opponents and move seven points clear of third-bottom NAC Breda.
Sebastian Steblecki's first goal since November gave Cambuur a 1-0 victory over beleaguered Go Ahead Eagles, who have now lost six in a row and remain 17th.
