McIlroy, the world No.1, chipped in for birdie on the final hole of his second group match at the Turkish Airlines World Golf Final yesterday, only for the South African Charl Schwartzel to follow him in from 12ft.
It meant a one-shot victory for the South African (70 to 71) and a second straight defeat for McIlroy, who must beat Tiger Woods and have Schwartzel beat Matt Kuchar to have any chance of making the semi-finals.
Those final group games were scheduled for yesterday afternoon but were called off because of a thunderstorm, so McIlroy must return to Antalya GC for at least 18 holes today.
"It was a decent match," said McIlroy. "I felt like I played a bit better, had plenty of chances and just didn't really hole much. Charl played solid and then birdied three of the last four so I couldn't really do much about that."
Schwartzel, hampered by various injuries this season, has beaten the world's top two players back to back and said: "Any time you can do that it's going to give you a lot of confidence."
Woods lost to Schwartzel on Tuesday but beat Matt Kuchar by five shots yesterday with a round of 67, four under par.
The scoring system – one point for a win in each 18-hole medal matchplay contest – means that all eight players still have a chance of reaching the semi-finals. Wins for Schwartzel and McIlroy would put Schwartzel through to the semi-finals on three points with McIlroy, Woods and Kuchar all on one point in Group 1. The lowest aggregate score for each player's three matches would be used to break the tie, with one joining Schwartzel in the last four.
The same scenario could also unfold in Group 2. Justin Rose is top with two points after beating Lee Westwood (66 to 69). Webb Simpson (65) joined Westwood on one point by beating Hunter Mahan (67). Rose faces Simpson and Westwood plays Mahan today.