So far in his first grand slam title defence, Andy Murray needed to beat players who are ranked 47th, 49th, 65th and 81st.
He's well aware things probably will get a tad tougher the rest of the way at the US Open, starting with No 9 Stanlisas Wawrinka in the quarter-finals.
"Hopefully I'll start playing a little bit better from now on. I mean, sometimes the first week of a slam, I've played very well. Sometimes you maybe feel like there's a little bit something to lose," said Murray, who is 30-2 over the past five major tournaments.
"I'm in the quarter-finals of a slam. It's not an easy thing to do, and the matches are going to get tougher," he said. "I'll have to up my game."
In a 6-7 (7-5), 6-1, 6-4, 6-4 fourth-round victory over Denis Istomin of Uzbekistan on a windy night, Murray found reasons to yell at himself for mistakes.
He faltered late in the first set, dropping four points in a row. He also flubbed what should have been a simple volley after Istomin's between-the-legs shot late in the second. There was more shakiness from Murray in the third set, in which he went up a break, only to lose serve to make it 3-3. But he broke right back for a 4-3 edge, and was back on his way.
Murray's back felt a bit stiff, he said afterwards, owing to the cold, windy conditions.
"I wanted to just try and get through the match," he said. "With the way the third set ended up going, I was just very happy to get it done."
He was 0-4 in grand slam finals until his title at last year's US Open. He added a second major championship in July by becoming the first British man since 1936 to win Wimbledon. Both times, Murray defeated Novak Djokovic in the final.
Murray leads the head-to-head series against Wawrinka 8-5, but they've split their two previous meetings on the US Open's hard courts: Murray won in 2008, and Wawrinka won two years later. Wawrinka won their only match this season, 6-1, 6-2 on red clay at Monte Carlo in April.
"To beat him," Wawrinka said, "I need to play my best tennis, that's for sure."
If Murray can get past Wawrinka, who eliminated No 5 Tomas Berdych 3-6, 6-1, 7-6 (8-6), 6-2, Djokovic might very well be waiting in the semi-finals. The top-seeded Djokovic, whose six major titles include the 2011 US Open, has yet to drop a set and won 45 of 53 service points while beating 43rd-ranked Marcel Granollers 6-3, 6-0, 6-0.
In his 18th consecutive grand slam quarter-final, which comes today, Djokovic will face 21st-seeded Mikhail Youzhny.
All eight men's quarter-finalists are from Europe: Serbia's Djokovic, Britain's Murray, Switzerland's Wawrinka, Russia's Youzhny in one half of the draw, and Spain's Rafael Nadal, David Ferrer and Tommy Robredo, along with France's Richard Gasquet in the other half.
Murray has now reached the quarter-finals in each of his last 10 grand slam tournaments. But Istomin, 65th in the world, pushed Murray hard and the Wimbledon champion was glad to have won.
"I was just very happy to get it done because he had chances at the end of the third set to get ahead," Murray said.
"It was extremely cold on the court, very windy. Often when you sort of heat up and then in between sets or if you have quite a long break, you cool down pretty quickly," he said.
"It was very, very different conditions to the last few days where it's been very humid and you have been sweating a lot," he added.
Istomin's decision to play the ball between his legs on three occasions, once when he had a perfectly playable shot, may have pleased the crowd but raised some eyebrows and surprised his opponent.
"I think it was 5-4 in the first set when he had a pretty easy shot. I personally wouldn't try something like that at that stage, but he did, and yeah, it was a bit surprising," Murray said.
Associated Press, Reuters