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.
A massive first prize of almost £840,000 is up for grabs and while 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.
That may have just delayed a head-to-head clash between golf's current top two for 24 hours, but Warren takes great heart from how he performed.
"Little things like that, it does wonders for your confidence," he added.
"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.
"When I came off the course I had a really sore head and fever," he said. "I just took painkillers and Caroline (girlfriend Caroline Wozniacki) squeezed about five lemons into a glass and I took that.
"I had some sort of vitamin and mineral drink too. It made me a feel a little bit better, but with the anti-doping and all that we can't really take much.
"I'm not feeling great again now, the sun's taking it out of me a bit."
This time last year McIlroy was told he might be suffering from Dengue fever.
"It's nothing to do with Dubai," he added. "It's something about this time of year; it's all the travel we do. All that time on planes is not great for you."
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.
This year's hopefuls, including Ryder Cup pair Paul Broadhurst and Jarmo Sandelin and fellow Tour winner Nick Dougherty, are gathered now in Spain and Grace was asked if he had a message.
"Good luck," he replied. "It's going to be a long week (six rounds), but if they have a think about what I've achieved then anything is possible.
"I was one of those guys last year, so things can change and it changes quickly."
Grace's 65 was not the round of the day. 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.
That came when he hit a six-iron approach into the water on the 16th and then three-putted, but he birdied the short 17th and sank a putt of around 18 feet for his second eagle on the last.
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.