The PGA Tour's latest foray into Mexico has produced a crowded leaderboard after one round. Here's how things look at the WGC-Mexico Championship, where Phil Mickelson is one of several first-round co-leaders:
What it means: There are only 76 players remaining in this week's event, but nearly a fifth of them are within one shot of the lead after the opening round at Club de Golf Chapultepec. The co-leaders include major champs in Mickelson and Walker as well as Rahm, arguably the hottest rising star in the game. Meanwhile McIlroy headlines the group just one shot back after a strong start to his first competitive round in more than a month.
Round of the day: Mickelson remains in search of his first victory since the 2013 Open Championship, but he's already put together some solid rounds this season at age 46. That trend continued Thursday as Lefty carded six birdies against two bogeys, closing with a 16-foot birdie on No. 18 to grab a share of the early lead.
Best of the rest: Rahm burst onto the professional scene with his win earlier this year at Torrey Pines, and he hasn't slowed down since. The Spaniard finished T-5 in his most recent start at Pebble Beach and is among the group at 4 under par after a 67 that included three back-nine birdies and only one dropped shot.
Biggest disappointment: The no-cut event lost one of its biggest draws when reigning Open champ Henrik Stenson withdrew during the first round because of a stomach bug. Stenson birdied his first two holes but was 2 over after 11 holes when he decided to withdraw, pocketing $43,250 in last-place money for his troubles.
Main storyline heading into Friday: Mickelson will remain a player to watch until he breaks out of his lengthy victory drought, but don't lose sight of McIlroy. The Ulsterman was one of the biggest question marks coming into the week, but he seemed to be near full strength during an opening-round 68 that he later revealed was also hampered by some late-night food poisoning.
Shot of the day: All Justin Thomas could do was shrug when his 103-yard punch-out from the trees on No. 4 improbably rolled up to the green, hit the stick and dropped. The unlikely birdie helped Thomas to a 2-under 69.
Quote of the day: "I was praying to the porcelain bowl." - McIlroy describing the stomach issues he suffered prior to the opening round.