McIlroy’s round included an eagle and six birdies but was let down by four bogeys as he dropped level with Tiger Woods, who made up a shot to reach 12 under after a bogey-free round of 67.
Singh recorded a round of 66 for a two-round total of 13-under 131, putting him one shot clear of first round co-leader McIlroy, plus Tiger Woods and Ryan Moore.
Lee Westwood produced one of the the best rounds of the day with a seven-under 65 to move to 11 under after two rounds, and his feat was matched by Pádraig Harrington, whose 65 left him two strokes further back.
Justin Rose’s disappointing 70 left him level with Harrington at seven under, a position also shared with former Open champion Louis Oosthuizen, with Luke Donald one further back on six under.
While McIlroy’s charge towards the $10m FedEx Series has earned high praise from countrymen, Damien McGrane and Peter Lawrie, playing at the centenary KLM Open.
England’s Graeme Storm (66) heads the Dutch event by three shots on 11-under par. Simon Thornton posted a 64 to share seventh place on five under par.
McGrane, who aced the par three third hole during practice, birdied four of his outward holes in a round of 67 to move to three under par on the Hilversum course.
One behind at two under par is Lawrie who capped a second round by holing his second shot, a 7-iron from 172 yards out, for an eagle at the par four, seventh hole.
And while McGrane and Lawrie may have contrasting goals as the season draws closer to conclusion, they continue to share a common opinion of McIlroy.
“It’s just unbelievable what Rory has accomplished this year and I always said when he first came out here, Rory was a superstar in the making and he continues to prove that,” said Lawrie.
“He’s just taken over from Tiger (Woods) big time and the way he plays the game is like how Tiger used to play, and it’s just amazing as Rory’s still only 23.”
McGrane said: “Rory’s just gone from strength to strength and I’ll be watching the Ryder Cup with much interest.”