Louis Oosthuizen leads the WGC-Mexico Championship after firing a 7-under 64 in Round 1 in Mexico City on Thursday. The former Open winner leads Chris Paisley, Xander Schauffele and Shubhankar Sharma by one stroke each. He had five birdies and an eagle on the day, and his clean card was nearly one better as he burned the edge on a long birdie on No. 17. Still, the 64 was impressive and stands as the second-best round shot at this event in its recent two-year history (Jordan Spieth shot 63 in Round 3 last year).

"I'm very confident with my driver at the moment," Oosthuizen told Golf Channel. "I've been swinging it pretty good the last 3-4 weeks. I'm hitting it well. I just need to do the same tomorrow. I hit a few really close."

Oosthuizen's swing looked gorgeous (per the usual), and he putted the lights out, gaining more than three strokes on the rest of the field with the flat stick. Oosthuizen has never won a WGC event and actually doesn't have a PGA Tour win outside of that Open victory in 2010. It's easy to envision him rolling from start to finish this week, but he'll have some stout competition with most of the top 50 in the world present this week in Mexico.

Here are five takeaways from Round 1.

1. Who is Chris Paisley? The Englishman is T2 after 18 holes and riding the heater of his life. Paisley played college golf at Tennessee and has made a decent living on a variety of worldwide tours. But he's really taken off recently as he won the South African Open (with his wife working as his caddie) to start January and finished in the top five at both the Abu Dhabi Championship and Dubai Desert Classic. This is his first-ever WGC event, and he's clearly fired up about getting to play with most of the best in the world (it's also not a huge surprise that he's contending as a European ... see below).

2. Justin Thomas struggles: Following a monster win last week at PGA National and the fallout of tossing a spectator near the end of his final round, Thomas couldn't get going on Thursday. He only made two total birdies, shot a 1-over 72 and finished outside the top 50 in strokes gained on approach shots. That's not a formula for winning a golf tournament (or one Thomas is used to).

3. Outrageous shots lead to low scores: I'm with Tommy Fleetwood -- this is a low-key awesome course, and a nice salve as the event following a rough Honda Classic. The score disparity in Round 1 was fascinating. Fifteen shots separate the leader and last place. The No. 3 player in the world was over par. It looked like a 59 was in play for Bubba Watson for a while. This to me is the sign of a good and fair track.

4. Jon Rahm donates $6,000 to charity: Speaking of Rahm, he racked up six big ones for the Mexican Red Cross with six birdies in his first round on Thursday (and tossed in a 4-under 67). He lit this place up last season and nearly took down Dustin Johnson coming home, so this wasn't exactly a huge surprise. He's such an overwhelming talent when he gets going, and it must feel downright impossible to hold him off when he starts picking off birdies on three straight holes like he did on Thursday. It'll be no surprise if he wins this week, and the Mexican Red Cross has somebody to root for on the weekend.

5. Where have all the Americans gone? Six of the top seven players through 18 holes are from outside the U.S. The only American in that group is Xander Schauffele. Sergio Garcia shot a 68, and he finished as the third-best (!) Spaniard on the day. As Paulie of the Fried Egg recently pointed out, this course actually sets up nicely for a more European style (Ross Fisher and Tommy Fleetwood performed very well here last year).

This week's course is similar to many European courses that place an emphasis on ball striking and punish wayward tee shots. I would favor European players who are used to playing a more precise type of golf as opposed to the modern American version of bomb and gouge.

That's not to say an American can't or won't win (D.J. took the trophy last year), but it might help explain the lack of stars and stripes at the top of the leaderboard.