He became the first Mexican winner in DP World Tour history at last season's WGC - FedEx St Jude Invitational and put on a masterclass against the World Number Two at Austin Country Club.
He was five up at the turn and did not take his foot off the gas as he sealed just the second win this week on the 12th green, maintaining his record of not having trailed in a match.
"Very pleased, especially if you can save any type of energy for the afternoon," he said.
"These days are very long and mentally it's tough and draining. So, yeah, very happy with my performance today.
"It's just being in the fairway and telling myself that I'm going against one of the best ball strikers in the world, maybe the best, so I had to hit the ball perfect and make some putts. So thankfully that was the case.
"I've had some nice feelings throughout my swing, throughout the week, that I wasn't really having the past weeks. But I knew I was really close and putting has also been really nice this week."
Ancer hit a smart approach to win the third with a birdie and made a two-putt birdie on the par-five sixth before putting his tee-shot on the par-three next inside three feet.
Morikawa bogeyed the eighth and ninth to put Ancer 5 Up at the turn and the 31-year-old holed a 25-footer at the 11th and made the most of the par-five 12th to cruise to victory.
Ancer will next face Corey Conners who was also a comfortable winner, beating Takumi Kanaya 5 &3.
The Canadian birdied the second and third and won the seventh with a bogey and, while Kanaya won the tenth, Conners birdied the 11th and 12th and sealed victory at the 15th.
Will Zalatoris survived a comeback from Kevin Na in a see-saw contest to beat his fellow American in a play-off.
A Zalatoris bogey had put Na 1 Up at the second but the 24th seed put an approach to five feet on the fifth to even things up and then put his second to 11 feet on the sixth and made an eagle.
A tee-shot to five feet at the seventh and a Na bogey on the next had Zalatoris 3 Up but Na cut the gap to two at the turn with a birdie on the ninth.
Zalatoris holed from 12 feet to birdie the tenth but Na is a steely competitor and he eagled the 12th from nine feet, birdied the next and took advantage of a Zalatoris bogey on the 14th.
Na led after a tee-shot to three feet at the 17th but Zalatoris got up and down from the sand on the last to take it to extra holes before a deft touch brought a birdie and victory at the fourth extra hole.
Kevin Kisner is next for Zalatoris after the 2018 finalist and 2019 champion fought back to beat Adam Scott 1 Up.
Scott won three holes in a row from the third but Kisner took the seventh and ninth to trim the gap to one at the turn.
Birdies at the 12th and 14th had the Australian 3 Up with four to play but Kisner birdied the 15th, holed a bunker shot for eagle at the next, was All Square as Scott bogeyed the 17th and then birdied the last to stun the former World Number One.