MIAMI, 7 Mar 2015 (AFP) - After a stunning 62 on Thursday, Holmes had a 36-hole total of nine-under-par 135, his four-shot overnight lead over Ryan Moore whittled to two strokes over his fellow American.
While Holmes keeps the lead, world number one McIlroy spectacularly lost his temper, so irked was he by hitting into the water at the par-five eighth that he slung his three-iron into the drink, in an uncharacteristic fit of pique.
The 25-year-old from Northern Ireland, who will try to complete a career Grand Slam at the Masters next month, made one of his four bogeys at the hole, countering with six birdies in a 70 that left him tied for 11th on one-under 143.
"Frustration got the better of me," McIlroy said. "I've sort of been fighting that miss basically for the last couple of weeks."
He stressed that he didn't think his behavior was anything to be proud of.
"It felt good at the time, but right now I regret it," he said. "I walked away with a bogey and I was able to regroup and shoot a decent score."
Holmes could no doubt relate to McIlroy's frustration. After five birdies and four bogeys he was one-under for the day when he arrived at 18, where his tee shot into the water led to a double-bogey to end his round on a sour note.
Moore carded a one-under 71 to remain alone in second place on 137, one shot in front of Australian Adam Scott, whose four-under 68 was the low round of the day.
Masters champion Bubba Watson carded a three-under 69 to share fourth on 140 with Sweden's Henrik Stenson, who posted a 71.
Leading second-round scores on Friday at the World Golf Championship Cadillac Championship at Doral in Florida (USA unless noted, par-72):
135 - J.B. Holmes 62-73
137 - Ryan Moore 66-71
138 - Adam Scott (AUS) 70-68
140 - Bubba Watson 71-69, Henrik Stenson (SWE) 69-71
141 - Dustin Johnson 68-73, Alexander Levy (FRA) 68-73, Ryan Palmer 71-70
142 - Jamie Donaldson (WAL) 70-72, Sergio Garcia (ESP) 73-69
143 - Webb Simpson 74-69, Jim Furyk 70-73, Lee Westwood (ENG) 71-72, Charl Schwartzel (RSA) 71-72, Brooks Koepka 69-74, Rory McIlroy (NIR) 73-70, John Senden (AUS) 73-70
144 - Charley Hoffman 70-74, Morgan Hoffmann 73-71, Gary Woodland 70-74, Patrick Reed 71-73, Jordan Spieth 75-69
145 - Shane Lowry (IRL) 71-74, Victor Dubuisson (FRA) 72-73, Louis Oosthuizen (RSA) 71-74, Rickie Fowler 68-77, Brendon Todd 72-73, Kevin Na 74-71
146 - Bae Sang-Moon (KOR) 75-71, Graeme McDowell (NIR) 73-73