World number one Andy Murray bemoaned his serving and movement after making a sluggish start at the Australian Open.
A five-time runner-up in Melbourne, Murray was far from his best as he overcame Illya Marchenko in the first round on Monday.
In warm conditions on Rod Laver Arena, Murray needed almost three hours to beat the world number 95 7-5 7-6 (7-5) 6-2.
Murray failed to convince from the outset, serving three double faults in the opening game before surrendering a break lead.
The three-time grand slam singles champion ended the match with a first-serve percentage of just 48.
Speaking in a news conference post-match, Murray told reporters: "I don't think it was the best match, to be honest.
"The conditions there were pretty different to what we've been practicing. Last week's been pretty cool. A lot of days, it's been overcast. The temperature of the court is much cooler. When it's like that, the ball is bouncing a bit lower, a bit easier to control the ball.
"I was a bit tentative because of that. Didn't serve that well either. So you end up having to work really hard on a lot of your service games when it's like that. It just was tough."
Murray continued: "I didn't move that well. That's how it felt anyway. But sometimes that can also be down to the conditions, as well.
"The ball's flying through the air a little bit quicker, so the ball is coming onto you faster than what it was the last few days. Maybe wasn't reacting as quickly as I would have liked.
"But maybe also nerves there first round as well. It's maybe normal to feel a little bit slow on your feet or a bit heavy-legged in the first round."
Competing at a grand slam as world number one for the first time, Murray - who has also received a knighthood - said he is embracing the top ranking.
"It's been great," he added. "I think because it's taken me so long to get there, obviously I want to try to stay there, but also I feel like I'm mature enough now to handle it.
"Maybe if it happens when you're very young, you might feel extra pressures, the responsibilities might feel a bit much. But I think because I'm much older and more mature, it's been good."