Spieth then found sand again off the tee at the last, but he clipped a short-iron to 20 feet and followed it with a flawless putt to regain the outright lead ahead of Weekley, who was just level par for the front nine before his putter caught fire after the turn.
Boo Weekley is right behind Spieth at 11-under 199 after a 65 in the third round.
Rory McIlroy, who barely made the cut on Friday, carved out a round of 70 on Saturday and is well off the pace at par for the tournament with a 210 total.
He came back with a birdie on 15 to grab the outright lead, but Berger, playing in the group ahead of Spieth, answered with a birdie on 17 and then parred 18 to take the clubhouse lead at 12 under.
The 51-year-old Englishman opened with a 63. 2, 10, 12, 13 and 18, two from between 17 feet and 26 feet, posting 1.714 putts per GIR and 1.822 SG: Putting. He hit his first shot on 15 in the bunker, but put the ball eight inches to the hole on his second stroke.
Meanwhile Americans Troy Merritt and Patrick Reed find themselves the closest in contention to Spieth, as the duo sit tied second just a shot behind the former world number one.
Ricciardo wins chaotic Azerbaijan GP; Vettel, Hamilton clash
Nothing happened did it...he brake checked me as well so what do you expect? "I don't run into the back of him on goal ". Further chaos unfolded when Daniil Kvyat stopped, his Toro Rosso having lost all electrical power on lap eight.
In the third round, Spieth was even par through five holes before a pair of birdies moved him to 10-under. Weekley hasn't won on the PGA Tour since Colonial in 2013, his last top 10 on Tour is a solo fifth at the 2016 Waste Management Phoenix Open and he doesn't have a top 25 on the circuit this season. The first was a second-shot 3-wood into a strong wind that went just over the green; the second was a flop shot that set up a 3-foot birdie putt. They each shot 66.
Tournament host Steve Stricker had a 69 to join Fred Couples (68) and Gene Sauers (66) at 9 under.
Stricker is making his first start in his hometown event after turning 50 in February. He tied for 16th last week in the U.S. Open at Erin Hills.
Fellow Madison player Jerry Kelly was tied for 11th at 6 under after a 70.
Guys on the PGA Tour are so generous with their time in supporting charities or other life-changing organizations that it's never a surprise to see the touching gestures they make around the world.
Garcia, playing his first event in Europe since his Masters win, and Bland settled at 13 under overall going into today's final round on Munich's Eichenried course. He also had four birdies and a bogey to reach 8 under.
Hoffman eagled the par-3 13th hole and followed with two birdies, but then his round fell apart with a double bogey at the par-3 16th hole and bogeys at Nos.