John Isner knows a lack of preparation was behind his shock second-round Wimbledon exit.

The 2018 semi-finalist, seeded ninth, looked on course to beat Mikhail Kukushkin as he was a set away from victory, but ended up falling to a 6-4 6-7 (3) 4-6 6-1 6-4 defeat.

Isner has not played any matches on grass prior to this tournament due to a foot injury and it came back to hurt him.

"It's very disappointing to lose," he said. "I think my lack of preparation certainly showed today.

"I knew something like that was very possible. Unfortunately, that was the case.

"It stinks going out early in this event, for sure. But it's not all bad. I go back home and I can really start to practice and work out and get myself back into better shape with each day."

Marin Cilic's horrible 2019 continued as the former finalist was beaten at the second round stage for the second year running.

The 2017 runner-up was beaten 6-4 6-4 6-4 by Joao Sousa on Court 12.

There were no such problem for Roger Federer, who beat British hope Jay Clarke in straight sets on Court One.

The Swiss was taken to a tie-break in the second set in an otherwise routine outing, but was impressed by Clarke.

"I liked what I saw in Jay," he said. "I don't know if grass is his favourite surface or not, it seems like he doesn't mind longer, extended rallies, so maybe grass is not his maybe number one surface."

Kei Nishikori also made it through it straight sets against a home favourite, dispatching Cameron Norrie in straight sets, while Sam Querrey and Steve Johnson were both American winners on Independence Day.