AUGUSTA, Ga. -- Even coming here with a series of bad results fresh in his mind, Phil Mickelson knew things were likely to change when he drove down Magnolia Lane.

Augusta National provides Lefty a freedom he feels is missing at regular PGA Tour venues, and that showed during a first-round 67 at the Masters.

Mickelson, 48, opened the tournament with his best first round since shooting the same score in 2010, when he won the third of his three green jackets. There is a long way to go, but a victory at the Masters would make Mickelson the oldest to win a major championship in the game's history, surpassing the record held since 1968 by Julius Boros.

"It was great. It was a lot of fun,'' said Mickelson, who is in third place, one stroke behind leaders Bryson DeChambeau and Brooks Koepka. "And it's fun to finish off the round. It's fun to make a good par save on 17 and birdie the last. It's fun to finish a good round off rather than leak one here or there coming in. So it was a good day.''

There had been few of those for Mickelson since winning the AT&T Pebble Beach National Pro-Am for his 44th PGA Tour title in February. In five events, his best finish was a tie for 37th, and he missed two cuts.

Two weeks ago at the WGC-Dell Match Play Championship, Mickelson lost each of his first two matches, rendering the final-day victory over Jason Day meaningless. But he immediately headed to Augusta and spent four days practicing here before heading home to San Diego, where the putting green at his home was set to lightning-fast pace to deal with the speed of the Masters greens.

"I was just hoping to shoot in the 60s," Mickelson said. "I thought there were some 66s out there. Look, the greens are softer than they've ever been, and they're not as fast as they normally are. So today was a day to take advantage of it. I'm sure they'll get firmer and faster as the week goes on. But you could get after the pins and you could putt aggressively."