This left the 23-year-old a whopping nine strokes behind leader Javier Colomo (28) of Spain and needing to dip well below par in his second round early today to avoid his first missed cut since last June's US Open.
Colomo was just one stroke clear of Jimenez overnight, with European Ryder Cup captain, Jose-Maria Olazabal, another Spaniard, claiming a share of fourth on four-under. Should Jimenez manage to win the Hong Kong Open for a third time on Sunday, this remarkably durable campaigner will replace Ireland's Des Smyth as the eldest tournament-winner on the European Tour.
Smyth was 48 years and 34 days old when he romped across mountainous terrain to victory at Santo de Serra in the 2001 Madeira Island Open.
Physically, the golf course at Fan Ling, the shortest on the European Tour this season, is not as challenging. Instead, its tight, tree-lined fairways and small greens look like a perfect fit for Jimenez, who celebrated his 48th birthday 316 days ago on January 5.
The cigar-chomping, rioja-drinking bon viveur works and shapes his ball expertly, which helps explain how he has been able to complete 12 of his 18 Tour victories since turning 40 and made the 2010 European Ryder Cup team.
"I've always enjoyed coming here," said Jimenez, winner of the Hong Kong Open in 2005 and 2008. "I feel comfortable out there and that's the main thing.
"It's an old-fashioned golf course," he added, "you're going to have flyers and the greens are fast. It's not very long, but you need to create shots and the par threes are phenomenal. I think it's a great course"
Jimenez signed for a five-under 65, despite making bogey on his final two holes, the ninth and 10th. After opening with three straight birdies, he was seven-under and cruising through 14 holes. "It was a pity to finish like that," sighed Jimenez, who has tumbled to world No 98.
Yet Olazabal, who showed with his own first-round 66 that he can still 'walk the walk' after brilliantly 'talking the talk' at Medinah, described playing with Jimenez as "inspirational."
Aussie Andrew Dodt, currently 122nd in the Race to Dubai and scrambling to save his European Tour card, was tied second with Jimenez.
However, the round of the day was the flawless 64 posted by Colomo, who has been tramping the Asian Tour fairways in 2012 with his wife Christina acting as his caddie. He's earned a respectable $102,000, good enough for 33rd place in Asia's Order of Merit.
He's 506 places behind world No 1 McIlroy in the current rankings. Yet the Holywood star performed well below his stellar best after losing his zip from tee-to-green and, frustratingly, with the putter as he landed just one birdie.
"I suppose after last week, and winning the Race to Dubai title, it was always going to be a bit of a let down," said McIlroy, who hit his ball so deep into trouble beside bushes on six, he had to flip-over his wedge and play the recovery shot left-handed.
"I feel as though I am playing well enough, but I just need to get my head and the golf to match-up and I'll be okay," added the Ulsterman, who wallowed in a share of 93rd place overnight.
Peter Lawrie, currently 60th in the Race to Dubai, boosted his prospects of playing in the elite 60-man field at next week's season finale, the DP World Championship, with a first-round 68.
This steady effort, which featured an eagle three at 13, placed the Dubliner in a tie for 17th with, among others, David Howell, ranked just one place behind him in the Race to Dubai.
Padraig Harrington posted an untidy one-over-par 71 after finding just six of Fanling's 14 fairways off the tee and hitting 11 greens in regulation.
Hong Kong Open,
Live, Sky Sports 2, 5.0am