The 29-year-old American shot a bogey free round of 66 and is two shots behind leaders Shaun Norris of South Africa and Italy's Renato Paratore.

Koepka, a four-time Major winner, had stem cell treatment on his left knee at the end of August but aggravated the problem when he fell over in October.

"It's good to be back," said Koepka.

"I missed the competition obviously and I played really solid. I missed a few putts early on, but drove the ball well and controlled distances really well - that's what you have to do out here."

Asked about his knee, Koepka told Sky Sports: "It feels fine. It was a little sore last night. That's expected. This is the first week I've walked 18 holes and I've done it three times already. It's a little tired."

Koepka, whose injury meant he had to withdraw from the United States team for December's Presidents Cup, produced a bogey-free round of six under.

Both Norris and Paratore hit nine birdies, but bogeyed the par-three seventh.

Norris, 37, said: "It will be a dream come true to win a European Tour tournament. I'm sticking to my guns. Stick to the same game plan and just go out there and have fun."

Two-time winner Tommy Fleetwood is seven shots off the lead after an opening 71, while 15-year-old English amateur Josh Hill - who beat Koepka in a practice match earlier this week - returned a two-over-par 74 and is tied 97th.