He's joined at the top by Matt Fitzpatrick of England at 4-under 206 at The Country Club in Brookline, Mass. Fitzpatrick shot 68 in the third round.
Defending champion Jon Rahm looked to be in position to hold the third-round lead until a double-bogey 6 on the last hole, unable to get out of a sand bunker that turned costly. He's alone in third, one shot back of the leaders.
Rahm went to the top of the leaderboard with a birdie on the 17th hole.
Zalatoris, 25, is contending in a major for the second month in a row after falling in a playoff to Justin Thomas in the PGA Championship.
Fitzpatrick led briefly late in the day with a birdie on No. 17. He fell back into a tie with Zalatoris, who already had finished his round, with a bogey on the final hole.
But Rahm wasn't finished, posting birdies on Nos. 14, 15 and 17 and appearing in good shape until a mess on No. 18.
First-round leader Adam Hadwin (70) of Canada, Scottie Scheffler (71) and Keegan Bradley (69) are tied for fourth at 3 under. Bradley, a Vermont native, is giving the tournament a particular New England flavor.
Sam Burns (71), Rory McIlroy (73) of Northern Ireland and Joel Dahmen (74) are all at 1 under.
Zalatoris, who was the 2021 runner-up at the Masters, tied for sixth in the 2020 US Open. He played the backside in 1 under Saturday.
Fitzpatrick already owns success on the course, winning the 2013 US Amateur at the site.
Zalatoris and Fitzpatrick were tied for second place after three rounds of May's PGA Championship in Tulsa, Okla.
Windy conditions created trouble for many golfers Saturday. Long sleeves were the order of the day for many on the course.
Scheffler took the lead on the eighth hole by chipping in for an eagle from about 100 yards. But he hit trouble spots with a double-bogey 5 on the 11th hole and bogeys on the next three holes.
Still, Scheffler made a difficult par-saving putt on the last hole to stay in the mix.
Collin Morikawa, who won the PGA Championship in 2020 and British Open in 2021, and Dahmen were the co-leaders at the midway mark through Friday's round. They experienced varying degrees of difficulty.
Morikawa was even through five holes, then suffered a bogey and double-bogey on the next two holes. He shot 77 and slipped all the way out of the top 15.
