Alex Fitzpatrick outshone his brother and two-time winner Matt on day one of the Omega European Masters at Crans-sur-Sierre.
Alex carded seven birdies in a flawless opening 63 to share the lead on seven under par with Spain's Alfredo Garcia-Heredia. England's Matt Wallace is part of a four-way tie for third on six under.
Matt Fitzpatrick, aged 30 and the older sibling by five years, won the title in 2017 and 2018 and is seeking to join the late Seve Ballesteros as a three-time champion. He returned a four-under-par 66 as the early starters battled cold and wet conditions.
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"Happy with a good start. I would have taken it this morning when I woke up and it was pouring," the 2022 US Open champion said.
"It's one of my favourite places to be but it wasn't really this morning. It was horrible; warming up in the rain and you get out there and it's pouring, you don't feel like the ball is going very far."
Alex Fitzpatrick, who finished tied for fifth on his debut at Crans-Montana last year, said: "I played really nicely.
"The first five or six holes were fairly brutal, I think it was gusting at 25-30mph or whatever it was.
"I got the nice side of the draw to be honest. This morning was brutal and luckily the last eight or nine holes there was not much wind, so it was nice to capitalise on the opportunities I had and hopefully the same tomorrow."
Wallace came into the week as one of the favourites after following an opening 76 in the British Masters with three straight rounds of 68 to finish eighth at The Belfry.
"Learning from last week and getting a lot of confidence from not having a great first round and turning that into a top 10 meant I know I don't have to have my best stuff every single day," Wallace said after a flawless 64.
"You are going to play tournaments where you don't play well one day. I just want the bad days to be where I can still be in contention because I know my good stuff is good enough at the moment.
"If I can just keep playing the way I played today and keep my head, then I'm in a good place."