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’s last major victory – that day.
Now the duo, separated by 188 places on the rankings, are tied for the halfway lead with world No 2 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 (today) 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 feel a little bit better, but with the anti-doping and all that we can’t really take much.”
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 (yesterday),” he said.
Sergio Garcia equalled the course record of 64 with a mind-blowing round of two eagles, nine birdies, and only four pars.
There was a 65 from Sheffield’s Danny Willett, who now stands just three shots off the leaders, while successive 69s mean Malton’s Simon Dyson is two shots further back.
Hull’s Richard Finch trails at the rear after rounds of 76 74.