I have only been this impressed with John Isner once before in his career. That was when he took Rafael Nadal to five sets in a first-round match at Roland Garros. His performance during these past few weeks, though, shows far more upside to him than that one match in Paris did.

Isner has essentially developed a decent baseline game in the span of the past few weeks. It has been incredible to see and really came out of nowhere.  Isner has improved all of his groundstrokes each year of his career. He has been getting better. But still, as of early this season, Isner was still well towards the bottom of the top 100 in terms of abilities on the baseline, and that is a generous assessment.

Starting in Cincinnati and continuing through the US Open so far, though, it has been like watching a different Isner. His movement is very good, and he is hitting strong shots when he gets to the ball. He still sprays errors, but overall both his forehand and backhand have been very solid.

It is not only that Isner has cut down on errors, though. He is using his groundstrokes to set up points. Even against Gael Monfils, an incredibly skilled shotmaker and strong baseliner, Isner was staying in rallies and waiting for his opportunities.

Isner is markedly better from the baseline than he was a month ago. There really is no other way to say it. He is using his shots to actually gain superior positioning in rallies. Before, his baseline game really only involved trying to avoid an error until his opponent made one first. Now he worked the points and took advantage whenever he had an opening.

Against Monfils, Isner came out strong. Monfils was not playing poorly, but Isner was simply in charge of the match. His serve was clicking, and his baseline skills dominated Monfils. He took the first set by breaking in the twelfth game and broke Monfils twice in the second set to take it 6-2.

Then, in the third set, the match went from entertaining to absolutely amazing.  The conditions were hot and humid, and the players were starting to get frustrated a little. Monfils got the crowd into it on his side, which is surprising enough in it own right because he was facing an American. Then, Monfils raised his level and started battling on Isner’s service games. Monfils won the third set and managed to hold his serve throughout the fourth set to force a tiebreak. Isner took the tight 4th-set tiebreak and the match.

While this match was incredibly entertaining, especially the final two sets, we really have to take away from it how outstanding Isner’s performance was. There is no shame in losing a set to Monfils.

Isner’s movement and ground game are at a level that we have not seen before in his career. He is playing even better than he did when he lost to Nadal in two tiebreaks in Cincinnati. If he can sustain this form, that fourth-round matchup will be very interesting indeed.