Although world number two US Open second seed Roger Federer has gotten in some practice during his matches so far at the Championships, he has yet to be tested.
Pulling away quickly to big early leads, he has had the chance to try out different tactics under match conditions. The Swiss has dropped just nine games through two rounds, facing only two break points and saving both of them. "It was on the easier side," he said after his win Thursday, "so I was able to mix it up, was attacking, was also staying back some. I was pretty much all-out attack as much as I could.
"Obviously, I have to manage that against different players when the score line isn't maybe so one-sided."
That could be the case on Saturday against 29th-seeded Philipp Kohlschreiber. The 31-year-old German has been a Grand Slam quarter-finalist, at Wimbledon in 2012. Kohlschreiber has 21 career wins against top-10 opponents. Then again, that's against 70 losses - but as both numbers show, he's plenty experienced in this environment.
Kohlschreiber is 0-6 against top-10 players in 2015, though, and 0-9 in his career against Federer. Kohlschreiber did push the Swiss great to three sets on grass at Halle this year, losing two tiebreakers.
Federer hasn't dropped a set in the first two rounds at the US Open since 2004, when he went on to win the first of his five straight titles at Flushing Meadows. The third round is where the draw typically gets harder - though in Federer's case, that means winning in four sets instead of three. "I've always enjoyed conditions here, the balls, the speed of the court, the atmosphere in the arena," the 17-time Grand Slam champion said.
"It's always worked very well for me. I think this year is another good year. Doing the right things on the court."
After coming from behind in the final two sets and saving a match point against Grigor Dimitrov in the hard-court warm-up tournament at Cincinnati last month, Andy Murray noted that a win like that could pay dividends in the future - and not just in his own confidence that he can rally from big deficits.
"I think other players look at matches like that and they see, Wow, he came back from a couple of breaks down in the second and 5-2 in the third," Murray said then. "Players look at that and you want to build up that sort of - it's not necessarily a fear, but more of a reputation that when you are behind that you're going to try to come back and you're going to fight all the way. If that's in the back of your opponent's mind going to a competition, that helps."
Murray gave his opponents something else to think about when he rallied from two sets down in his second-round match against Frenchman Adrian Mannarino on Thursday. So all that will likely be in the back of 30th-seeded Thomaz Bellucci's mind when they close out the night session at Arthur Ashe Stadium on Saturday. What will help Bellucci is he's 1-0 against Murray, though that win came more than four years ago and on clay.
With seven of the top 10 seeds already gone from the women's draw, some veterans who have fallen out of the top 10 could be in position to take advantage and use their experience to make deep runs.
But first they need to get by each other.
Two-time Australian Open champ Victoria Azarenka faces Germany's Angelique Kerber, twice a major semi-finalist who has been ranked as high as fifth. Azarenka is 4-0 against Kerber, dropping just one set.
In another intriguing third-round match-up on Saturday, Sam Stosur, the 2011 US Open winner meets 2012 French Open runner-up Sara Errani.