Tiger Woods says Rory McIlroy "made it look very easy" after the Northern Irishman set the early pace on day one of the US PGA Championship.
Seeking a first major in eight years, McIlroy carded five-under 65 to take a one-shot lead into the clubhouse at Southern Hills on Thursday.
The 33-year-old, who won this event in 2012 and 2014, closed with a birdie on the final hole – his seventh of the day – to put himself in strong contention for another title.
He teed off in a marquee group alongside Jordan Spieth and Woods, who carded 74 and 72 respectively, with the latter impressed by what he saw from McIlroy.
"Obviously you can shoot something in the mid-60s, Rory proved that today," Woods told Sky Sports. "He made it look very easy.
"He had a couple of shots where he slipped away and he still shot five under and made it look very easy."
McIlroy, who finished second in last month's Masters after shooting a record-equalling eight-under 64 on the final day, is not getting carried away just yet.
"I came in here knowing that my game was in good shape," McIlroy said. "So it's just a matter of going out there and executing the shots that you know that you can.
"Today I did that very well and I just need to try to replicate that tomorrow, Saturday, Sunday and not get ahead of myself, but it was a great start."
While McIlroy is in a strong position, Woods faces an uphill battle to make the cut, as he did at the Masters last month, but he is not giving up hope of a big recovery on Friday.
"It can be done, I've witnessed it first-hand, so hopefully I can put together something similar tomorrow and get myself back in this tournament," he said.
The 15-time major winner is competing in just his second tournament since sustaining serious leg and foot injuries in a car accident 15 months ago.
Woods felt some discomfort towards the end of an erratic opening round, which ended with him nine strokes behind McIlroy.
"Physically, I've felt better," he told Sky Sports. "Emotionally, I've actually felt better too.
"It was frustrating. I got off to a great start today, I did exactly what I needed to do starting out the round, but I did not keep it going.
"I hit a lot of bad iron shots, put myself in a lot of bad spots and never really gave myself any birdie putts.
"I actually felt comfortable with the driver, I hit a lot of fairways with it, but from there it wasn't very good. Most of my bunker shots I hit were long, came out hotter than I thought.
"But predominately I just hit bad iron shots. That's not normally how I play, but today unfortunately that's kind of what it was."