Playing partners Jason Dufner and Rickie Fowler also watched in disbelief when the 25-foot birdie putt lipped out.
"Unlucky," Dufner said. "He was walking it in."
"I thought it was in," Fowler said. "I was pulling for him."
Mickelson settled for an 11-under 60 at TPC Scottsdale, matching the tournament record he already shared with Grant Waite and Mark Calcavecchia.
Seeking his third victory in the event, Mickelson had a 4-stroke lead over Ryan Palmer, Brandt Snedeker, Padraig Harrington, Ted Potter Jr., and Jeff Maggert when play was suspended because of darkness in the round that started an hour late because of frost.
Singh's deer-antler fix
Vijay Singh withdrew from the Phoenix Open on Thursday, a day after saying he used deer-antler spray and was "absolutely shocked" that it may contain a banned substance.
Singh cited a back injury in pulling out before the first round.
In an interview with Sports Illustrated, the 49-year-old acknowledged paying $9,000 in November to Sports With Alternatives To Steroids for the banned spray, hologram chips, and other products.
DUBAI, United Arab Emirates - Richard Sterne nearly broke the course record at the Dubai Desert Classic on Thursday, shooting 10-under 62 in the first round to finish one shot ahead of Stephen Gallacher.
The 165th-ranked South African, who has struggled in recent years with back problems, started with three birdies on his first four holes. Sterne was on pace to break the course record of 61 set by Ernie Els in 1994, but couldn't convert late birdie chances.
Scott Jamieson, Chris Doak, and Tommy Fleetwood shot 65s. Paul Casey was another stroke back, while Lee Westwood shot a 67, five behind the leader. Sergio Garcia, who finished second last week in Qatar, shot a 68.