Warren remembers being paired with McIlroy at Walton Heath in a US Open qualifier; "I think he was about four at the time," he joked. It was actually 2008 and the 19-year-old McIlroy was already destined for greatness, but both failed to get through to Torrey Pines - scene of Tiger Woods' last major victory - that day.
Now the duo, separated by 188 places on the rankings, are tied for the halfway lead with world number two Luke Donald at the DP World Tour Championship. It could be McIlroy's fifth victory of the season or Donald's fourth - and second in a row - former World Cup winner Warren is hoping to end more than five years without a title.
"Everyone knew from day one that Rory was special and I'm really looking forward to it," said the 31-year-old after outscoring 2001 Walker Cup team-mate Donald by one with his second round of 67.
"It's going to be a great weekend. The atmosphere is buzzing already so I'm looking forward to seeing what it's like tomorrow and Sunday as well. It's nice to be the Scot with the Englishman and the Northern Irishman. It's a high-quality leaderboard and doesn't get any better in the world really."
McIlroy also managed a 67 after fighting with what he thinks was a touch of sunstroke following his opening 66. Donald lost the outright lead with his 68, but still has a chance to be the first player since Jesper Parnevik in 1995 to go through a European Tour event without a bogey.
"I haven't dropped a shot in 36 holes so feel good about that, but I wasn't as good on the greens today," he said. "I had some opportunities but that was a solid round. I thought the course played a little bit tougher. I didn't put myself in too much trouble and when I did I was able to recover with the putter."
Only a stroke behind are South Africans Louis Oosthuizen and Branden Grace, the latter chasing an incredible sixth victory since coming through last December's qualifying school.
Sergio Garcia equalled the course record of 64 with a mind-blowing round of two eagles, nine birdies, only four pars - none of them on the back nine - two bogeys and a triple-bogey seven. Not bad for someone playing their first tournament since undergoing laser eye surgery to correct astigmatism following the Ryder Cup in September.
Garcia still has four shots to make up, but that is four fewer than Lee Westwood, who double-bogeyed the 17th in a 74. In the 56-strong field only fellow Englishman David Lynn scored worse with a 77.