Watson became the first three-time winner on the PGA Tour this season, and pulled within one of Billy Casper's tournament record of four victories.
Watson also came from six back to win the 2010 event for his first tour title, and beat Casey in a playoff in 2015. The left-hander also won at Rivera in Los Angeles in February and the World Golf Championships-Match Play in Texas in March. He earned $1.26 million for his 12th career victory.
Watson shot a 33 on the front nine, but really got it going on the back, with five birdies. He tied Casey at 16 under by getting up-and-down from the bunker for a birdie on the course's signature 15th hole.
Still tied on the par-4 18th, Watson hit his tee shot 366 yards, then pitched inside 3 feet, giving caddie Ted Scott a big high-five before taking the lead with the putt.
American Family Insurance Championship
Scott McCarron won the American Family Insurance Championship, closing with an 8-under 64 for a one-stroke victory over hometown player Jerry Kelly.
McCarron birdied Nos. 14-16 and parred the final two for his first victory of the season and seventh in three years on the PGA Tour Champions. He finished at 15-under 201 at University Ridge.
Kelly shot 65, also parring the final two holes.
Fellow Madison player Steve Stricker, the tournament host and first-round leader, had a 65 to tie for third with 2017 champion Fred Couples and Colin Montgomerie.
Couples had a 67, playing alongside McCarron. Montgomerie followed a second-round 72 with a 64.
Second-round leader Esteban Toledo had a 73 to tie for 24th at 8 under.
NW Arkansas Championship
Japanese teenager Nasa Hataoka ran away with the NW Arkansas Championship on for her first PGA Tour title
The 19-year-old Hataoka won by six strokes, closing with an 8-under 63 at Pinnacle Country Club for a tournament-record 21-under 192 total. She broke the mark of 18 under set last year by So Yeon Ryu.
Hataoka began the round tied with Minjee Lee for the lead.
Austin Ernst shot a 65 to finish second. Lee and Lexi Thompson topped the group at 13 under.
BMW International Open
England's Matt Wallace shot a 7-under 65 to hold off Thorbjorn Olesen's record-breaking charge in the BMW International Open.
Wallace won his third European Tour title. He finished at 10-under 278 — a stroke ahead of Olesen, Mikko Korhonen and 2008 winner Martin Kaymer.
Olesen played himself into contention with a 61, the lowest round in tournament history. The Danish star had an eagle and nine birdies. Korhonen shot 67, and Kaymer 68.
WICHITA, Kan. (AP) — Brady Schnell birdied the second hole of a playoff to win the Wichita Open for his first Web.com Tour title.
The 33-year-old former Nebraska player made a 12-footer to beat Brandon Hagy.
Schnell won his 100th tour start, closing with a 4-under 66 to match Hagy and Scott Pinckney at 14-under 266 at Crestview. Hagy finished with a 63, and Pinckney shot 68.
Pinckney was eliminated on the first extra hole.
Schnell earned $112,500.