Record-breaking Rahm surges in pursuit of Finau at PGA Tour Mexico Open
Spain's Rahm, the defending champion, matched his career-best PGA round score, barely putting a foot wrong in a round that featured 10 birdies without a bogey for a course record at Vidanta Vallarta.
"Today, everything just seemed perfect," Rahm said. "Made a lot of great swings and the ones that weren't great, still gave myself a good result."
Finau, who started the day with a one-shot lead, didn't bow to the pressure, carding a six-under-par 65 for 19-under 194 and a two-shot lead over Rahm and 21-year-old American Akshay Bhatia.
Bhatia had eight birdies and an eagle at 18 in his eight-under-par 63 to join Rahm on 17-under.
Rahm, making his second start since he claimed a second career major at Augusta National this month, started the day six adrift but wasted no time in making up ground.
He rolled in a 39-foot birdie putt at the first and a 26-footer at the second before rattling in a birdie from two feet at the fourth.
He birdied three in a row from the sixth through the eighth, then put together another burst of three at the 12th, 13th and 14th, where he sandwiched birdie putts of seven and five feet around a 24-footer.
With a possible sub-60 round in sight, Rahm parred the 15 and 16 - missing a seven-footer at the latter.
He rolled in a 37-foot birdie at the par-three 17th, but his hopes of bettering his own career-best were dented when his tee shot at the par-five 18th ended up under the lip of a fairway bunker.
He had to punch out and his 30-foot birdie putt never threatened the hole.
Rahm said he couldn't be too disappointed after a round in which he rolled in putts totalling more than 156 feet.
"The fact that I made three putts over 30 feet - one is already a great bonus, to do it twice, three times, is amazing," he said.
Aggressive mindset
Rahm said he didn't focus on the fact that he was closing in on a possible sub-60 round but was just trying to keep pace with Finau.
"I know I was behind so I knew birdies were the only thing I had in mind," he said. "I tried to stay as aggressive as I could and I did a really good job at that."
Finau, who finished tied for second behind Rahm at Vidanta last year, opened with a birdie at the first and tapped in for another at the seventh.
A chip to two feet set him up for a birdie at the 12th and he chipped in from the greenside rough at the par-three 13th before making it three in a row with a birdie at the par-five 14th.
That put him one ahead of Rahm, and he padded that lead with birdies at 16 and 18 around his only bogey of the day at 17.
"The highlight was the chip-in on 13," said Finau, who is chasing his sixth PGA Tour title. "I hit a great chip on 12 to get it to tap-in and then missed the tee shot on 13, so I thought that gave me some nice momentum on a day where I was hitting it really nicely, wasn't getting that much out of my round."