British Open debutant Alex Fitzpatrick says he has a fiercer rivalry with golfing girlfriend Rachel Kuehn than he does with his famous older brother Matt after posting a stunning 65 on Saturday.

Alex, 24, will start Sunday's final round at Royal Liverpool at four under par -- two shots better than his US Open-winning sibling, who is ranked ninth in the world, 552 places higher than him.

But the competition between the two British players is nothing compared to that which Alex has with his girlfriend, an American amateur who is playing in next week's Evian Championship.

"There will be no rivalry or anything like that," said Alex. "We're brothers at the end of the day as much as we're golfers.

"I root for him, he roots for me. We're both supporting each other, and we both want what's best for each other.

"I don't get to play with him very often, so it's hard to beat him when you only played about three events in your lifetime together."

Asked where the bigger rivalry was he added: "Definitely the girlfriend, yeah, 100 percent. Lots of chipping comps, lots of putting comps.

"She claims she wins all the time, but she knows the truth. She's an amazing player. She has her own game."

Parents Russell and Susan have found their time divided this week but 28-year-old Matt, the 2022 US Open winner, has insisted they watch Alex in his first major.

"It's a difficult one because they've been to so many events with him (Matt). He plays every major, every PGA Tour event each week," said Alex.

"It's difficult for my mum and dad to come see me that often with the Challenge Tour.

"I think they thought they'd choose me today and it might be him tomorrow and that's fine. No drama or anything."

Matt felt it was only fair his parents focused on Alex this week as they were beside him for his major breakthrough at Brookline last year.

"I told them to go focus on him. That's more important," he said. "This is his first, so that's more important.

"They were going to do (that) anyway. I think they caught a few of my early holes and got back to watch him."

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