Ten of the 11 golfers who broke par on the 6,973-yard, par-71 layout were among those in the afternoon wave.

That included Mark Hensby and 68-year-old Jay Haas, both of whom carded four-under-par 67s to share the lead. Haas, playing in his 17th U.S. Senior Open and 50th USGA championship overall, shot his age for the second time this year, and joined four others to do so in the U.S. Senior Open.

“No, we got a lot lucky,” said Haas, a three-time senior major champion who has never missed a cut in the U.S. Senior Open, when asked if the 78-player afternoon group got the luck of the draw. “That was a big, big plus. I guess playing in the rain, the ball maybe goes a little shorter and everything, but it's just the whole hassle of the umbrella and towels and keeping everything dry. That's the thing that makes everything difficult.”

2019 champion Steve Stricker, 2008 U.S. Open runner-up Rocco Mediate, Paul Broadhurst and Tim Petrovic each carded 68s.

Only Paul Goydos (69) managed a sub-71 round among the morning group, as Mother Nature dumped nearly a half-inch of rain on the property. Afternoon starter Rob Labritz, a former club professional and a PGA Tour Champions rookie, joined him on that number.

RIGHT: It was all smiles for Jay Haas on day one of the U.S. Senior Open. PHOTO: USGA.

Four others from the morning wave shot even-par 71, including defending champion Jim Furyk, two-time U.S. Open champion Retief Goosen and three-time major winner Padraig Harrington, who is making his U.S. Senior Open debut.

“I'm from California,” said Goydos, a five-time winner on PGA Tour Champions who is affectionately nicknamed “Sunshine” for his dour sense of humour. “This is more rain than we've had in 10 years, it seems like.

“I'm really not a big fan of playing in the rain. I'm the guy who wants to play on domed golf courses.”

Players in the afternoon wave encountered relatively docile conditions. As long as competitors kept their golf ball out of the thick and moistened rough, good scoring was possible.

Hensby, who turns 51 on Wednesday, took full advantage, registering six birdies against two bogeys. In his Senior Open debut last year at Omaha Country Club, the youngest competitor in the field played only 10 holes before withdrawing due to a medical issue.

“Just training and practice, and hopefully when it comes [time] to go, you're ready to go.” - Mark Hensby.

The owner of six professional wins, including the 2004 John Deere Classic on the PGA Tour, doesn’t have full-time status on any Tour. He did tie for eighth in last month’s KitchenAid Senior PGA Championship, and he qualified in Pearland, Texas, for the U.S. Senior Open. He also played the PGA Tour event in Puerto Rico in March.

“Just training and practice,” said Hensby, “and hopefully when it comes [time] to go, you're ready to go.”

Haas doesn’t grind like he used to, but he still loves to compete. Earlier this year, he teed it up with son, Bill, in the PGA Tour’s Zurich Classic, a team event where he became the oldest player to make a cut in Tour history. Although he has never won the U.S. Senior Open, he does have five top-10 finishes. Last year in Omaha, he was tied fourth going into the weekend before finishing tied for 40th.

“I tell people that I still have a real passion to play the game, and I think that's helped me as much as anything,” said Haas. “Shooting my age is great. It's a good goal to have because that's a nice number certainly at a USGA event. Anything in the 60s is always really nice.”

Goydos’ performance arguably was one of the best of the day, considering the conditions. The rain, which came down hard at times, rarely let up from around 7:30 a.m. to when the afternoon wave started at 12:30 p.m.

“The bad weather tends to keep you a little more focused,” said Goydos. “Every once in a while, you're playing a golf tournament and you've got a 50-yard-wide fairway, and you may be at 90 percent instead of 100 percent. The USGA doesn't allow that. Their golf course setup is to penalise the guy that loses that little bit of focus, and I would say the weather kind of makes it a little bit easier to make sure you're there on each shot.”