Jimenez is two shots ahead of Alex Cejka and Mario Tiziani at Royal Porthcawl. Vijay Singh and Jeev Milka Singh are three shots off the lead.

"I am playing very solid on all parts of the game, from the tees to the greens, putting working also," Jimenez said.

Jimenez – who edged Bernhard Langer by one shot at St Andrews in 2018 – made six birdies and one bogey.

"I was little bit rushing myself there," he said of his bogey on the 14th.

"That was the only bad thing."

Defending champion Darren Clarke's 73 included a double bogey on the par-4 opening hole.

Langer – who won the last Senior Open held at Royal Porthcawl in 2017 – also carded a 73. He is a four-time winner of this major and has been runner-up three times.

Richard Green and Rod Pampling (both 72) are the leading Australians at one-over.

The tournament is the last of five majors on the senior schedule. The winner gets into The Open Championship next year at Royal Troon.