American Billy Horschel took the outright lead but a late flourish of birdies catapulted Rory McIlroy into a tie for fifth just three shots back after the second round of the Texas Open on Friday.
McIlroy, who would take the number one ranking back off Tiger Woods with victory, fired a five-under 67 at TPC San Antonio to roar up 40 spots on the leaderboard to five-under 139 in his last warmup for The Masters.
Horschel, who would gain a first invitation to Augusta National with a win, overcame two bogeys in his opening four holes to shoot a 68 for an eight-under total of 136.
The 26-year-old finished tied for second at the Houston Open last week and continued his hot form as he bids to enter a second major championship.
Fellow Americans Charley Hoffman (67) and Daniel Summerhays (69) along with Australian Steven Bowditch (69) are just two back in a tie for second.
Two-time major winner McIlroy's round was just his third sub-70 effort of the season.
At just one-under through 10 holes, McIlroy rallied with a birdie on the 11th and closed out the round with three more in succession to be right in the mix for the weekend.
Horschel overturned bogeys at the first and fourth holes with a string of three birdies on five, six and seven before gaining further strokes on the 14th, 17th, and 18th to jump clear.
Major champions Jim Furyk (70), Lee Janzen (69) and Retief Goosen (69) joined McIlroy in fifth at five-under along with Zimbabwe's Brendon de Jonge (69), South Korea's K.J. Choi (67) and American Ben Kohles (70).
Germany's Marcel Siem, a winner on the European Tour last week who lies just short of a direct Masters invitation at 51st in the world rankings, rebounded from an opening round 76 with a 67 to keep his slim Augusta hopes alive.
Former Masters champion Charl Schwartzel just scraped into the weekend on the cut line at one-over along with British world number 12 Ian Poulter.
They were joined on the cut line by last week's Houston Open champion D.A. Points and defending Texas Open champion Ben Curtis.
(Reporting by Ben Everill; Editing by Ian Ransom)