Justin Rose admitted two-time reigning champion Brooks Koepka's name is looming large at the halfway stage of the U.S. Open.
Englishman Rose posted a second-round 70 to maintain his position atop the leaderboard in California on Friday.
Koepka (69) – seeking a third successive U.S. Open crown – ended the round three shots adrift of Rose, who is wary of the world number one at Pebble Beach.
"He seems to get very focused. He seems to let the mistakes roll off his back," Rose told reporters. "I've heard him saying that so I'm just regurgitating that.
"I imagine it's a good start for him. He looked rusty in Canada, and come here, it's a great first couple of days. He's probably feeling like he can build into the week and put a good weekend together.
"And no doubt, him on the leaderboard, with his recent form in majors, absolutely. He's a threat. He is the guy probably that his name is standing out more than anybody else's, for sure."
After opening the tournament with a 65, 2013 champion Rose went one under on day two to be seven under through 36 holes.
Rose birdied two holes on the back nine before the turn, which yielded a birdie in between a pair of bogeys.
"Often the golf course gets tougher for the leaders in the afternoon so I've always felt like there's an opportunity and a mindset that just hanging around," Rose said. "Obviously wait for your run. And it's going to be the same for me in contention.
"Even if I'm in the lead it's going to be about being very patient but still waiting for my run, still trying to hit positive golf shots, still looking for the momentum. And just working really hard and fighting really hard if you're out of position. Each save can mean a lot come Sunday."