Phil Mickelson on Tuesday moved into even better position to win in his PGA Tour Champions debut.

Building on his opening 61, Mickelson fired a second-round 64 that gave him a four-shot lead at the Charles Schwab Series at Ozarks National. Mickelson is at 17 under par, four clear of Rod Pampling and Tim Petrovic, heading into the final round of the 54-hole event in Ridgedale, Missouri.

Mickelson's 125 total through two rounds is the second-lowest in tour history. Only Bruce Fleisher's 124 at the 2002 RJR Championship was better.

Averaging 340 yards off the tee, the newly 50-year-old added eight more birdies in the second round. After going out in 31, Mickelson made his lone mistake of the day on No. 10 before following up with three birdies in his next four holes. He’s now recorded the lowest score in each of the first two rounds.

Mickelson said he started working at home with putting guru Derek Uyeda and he has “started getting a lot of feedback on how I want the stroke to be.”

“When I get on the course, my feels start to equate and do what I’ve been expecting,” he said. “I’ve been putting really well.”

A 44-time PGA Tour winner, Mickelson is looking to become the 20th player to win in his senior debut.

Tee times have been moved up Wednesday in anticipation of afternoon thunderstorms. Final-round coverage will begin at 1 p.m. ET on Golf Channel.