Nadal had to fight off more break points but Kukushkin finally broke for a 3-1 lead as Nadal hooked a forehand wide after being taken out of his comfort zone - something Kukushkin did well throughout the match.
"This is gonna give me a lot of confidence for Wimbledon", Federer said. Between sets I needed that time to change all this stuff because it was a very humid day.
"No problems with him".
"For me personally it was disrespectful".
"I do my best to be quick".
Novak Djokovic reached an impressive landmark during his second-round win over Argentina's Horacio Zeballos, winning his 60th match at Wimbledon. Their second-round match was halted by rain on Wednesday with Fabbiano leading 7-6 (7), 6-3, 5-6.
Steven Gerrard says England won't get better World Cup finals chance
The Tottenham striker is also level with Gary Lineker's England record from the 1986 World Cup as he leads the race for the Golden Boot.
Asked if he had any doubts about being fit for Wimbledon's third round, Queen's Club runner-up Djokovic said: "No". It affected my knee a little bit. It is timed for release as the anticipation crests with Roger as returning champion, 10 years after their famed 2008 Wimbledon championship - an epic match so close and so reflective of their competitive balance that, in the end, the true victor was the sport itself.
"I've been doing check-ups now".
"Hopefully it's nothing that will concern me, so to say, that I'll be able to perform".
Fifth seed Juan Martin del Potro swept past Feliciano Lopez 6-4 6-1 6-2 in less than two hours, teeing up a clash with France's Benoit Paire, who beat 26th seed Denis Shapovalov 0-6 6-2 6-4 7-6 (7/3).
World number one Rafael Nadal will look to capitalize on his great start to the Wimbledon campaign when he squares off with Russian tennis player Mikhail Kukushkin in the second round of the men's singles event here on Thursday.
Highly-rated American Frances Tiafoe edged out France's Julien Benneteau 4-6 6-3 6-4 6-2.