Lucas Glover and Zac Blair set early pace at John Deere Classic with matching 63s

Johnson, who chose to play in Illinois instead of competing in this week's U.S. Senior Open, eagled the par-five 17th before closing with a birdie for a 64 to join Stephan Jaeger and Lee Hodges in a tie for third.

The 50-year-old, a two-time winner on the PGA Tour Champions this season, said there was never any doubt about returning to an event he won in 2012.

"I just love being here, and I'm comfortable, obviously," Johnson said. "I'm just appreciative of having a partnership with John Deere... A lot of affinity, a lot of affection."

Johnson is also skipping both The Open at Royal Birkdale and the Senior Open at Gleneagles, opting instead to play next week's senior major at Firestone as he did not want to compete for four consecutive weeks.

Glover's opening 63 was an encouraging return to form after shoulder surgery earlier this year. The former U.S. Open champion is currently 119th in the FedEx Cup standings and needs a strong finish to the season to retain his PGA Tour status.

"Even struggling like I have this year, you pull down the driveway somewhere you've had success, it gives you a good feeling," Glover said. "Yeah, always liked it here."

Blair, ranked 160th in the FedEx Cup, has split his season between the PGA Tour and Korn Ferry Tour as he fights to improve his standing.

"Every start is important," Blair said. "Just trying to do a good job of playing well, whichever kind of tour I'm playing on."

Elsewhere, Jordan Spieth opened with a two-under 69 after mixing five birdies with a double bogey and a late bogey.

Scoring was low throughout the opening round, with 20 players posting rounds of 66 or better. Amateur Preston Stout, the new world No. 1 amateur following Jackson Koivun's move to the professional ranks, was among that group with a 66, while Koivun struggled to a 73 on his professional debut.