After the first round of the Genesis Open at Riviera, Patrick Cantlay and Tony Finau co-lead at 5 under with a collection just behind them at 4 under and 13 players total within two strokes of the lead. Finau and Cantlay, two extraordinary ball-strikers, combined for 12 birdies and just two bogeys in some tough conditions at Riviera.

It was as eventful of a day as we expected, although the very end was suspended for darkness. Phil Mickelson and Justin Thomas got in the mix early. Rory McIlroy hung around. Tiger Woods shot a 1-over 72 that was somehow both better and worse than it looked. Jordan Spieth shot even par to match McIlroy. And, surprise of all surprises, Dustin Johnson faded hard with a 74 that included a gross triple bogey early on.

As the leaderboard starts to take shape on Friday and beyond, the cream will certainly rise to the top at this event (something we're already starting to witness). Here are five takeaways from the first 18 holes of the Genesis Open.

1. Scoring average was 1-over 72: Riviera is awesome for a number of reasons. At the forefront is the fact that it can both play easy (Dustin Johnson was 17 under last year) or tough depending on the weather. 

The wind blew a little on Thursday and players struggled at times. Guess what, that's fun. Watching the best players in the world make difficult decisions, trade out clubs and hit world-class golf shots is what I'm here for, and several of them did it on Thursday. The wind is supposed to die a bit on Friday, but hopefully the course is protected throughout the weekend so something like 8 under or 9 under wins on Sunday.

2. D.J.'s struggles: I came into this week thinking there's no way he's not going to finish in the top five (he's finished in the top four in four straight tournaments here). Then he made a triple at his fifth hole of the day, and away we go. Johnson finished with a 3-over 74 that could have been much worse. He played his last 13 holes in even par, but is currently outside the top 100.

The result? It seems like, as Will Gray noted, that his bizarre streak of either finishing in the top 10 at this event or missing the weekend altogether will roll on (remind me of this when he shoots 68 on Friday to make the cut by one).

3. Phil Mickelson's frustrated 70: Lefty is not normally one to emote outside of the occasional "how in the hell did that not go in" looks on a putt or chip shot. On multiple times on Thursday, though, he grabbed his cap or a club in frustration. It was actually odd to watch. But I think it speaks to where his game is at right now. Mickelson knows he's playing well enough to win every tournament he plays, so any missed opportunity or silly mistake seems like a bigger deal than it actually is. 

One other interesting note on Lefty's first 18 holes: He finished in the top 20 in driving and outside the top 100 in both around-the-green play and putting. I bet that hasn't happened in a long, long time.

4. Let's talk about Cantlay and Finau: I predicted that both (!) would make the Ryder Cup team in September, and we're off to a nice start this year. If you haven't been paying attention for the last year, these are two of the better swingers of the golf club in the world. Both quietly finished in the top 15 in strokes gained from tee to green in 2016-17, and both are made for a track like Riviera. 

Finau finished second from tee to green on Thursday, and Cantlay finished fourth. That's what you'd expect from co-leaders of this tournament on this track. They both have staying power, which means it's going to be difficult for anybody too far back to play catch up over the final three rounds. The board is bunched tightly enough that Vegas still gives Justin Thomas 12-1 odds to win the event, but these two leaders are clearly your two favorites after 18 holes.

5. Justin Thomas takes the premiere group competition: J.T. bested playing partners Rory McIlroy (by two) and Tiger Woods (by three) as he shot a 2-under 69 on Thursday. That threesome made up one of the best early-tournament groups we've seen in recent years (and maybe ever), and it resulted in a fascinating result for Woods.

But it was Thomas who was top dog. He couldn't have hit it more poorly off the tee, but his short irons were on point for most of the morning. After all three golfers in that group birdied their first hole of the day, it was only Thomas who kept it under par the rest of the way, mostly with shots like this.