John Isner splits with coach Craig Boynton

John Isner has split with his coach Craig Boynton after a three-year professional relationship.

The 6'9" American will now work with Monica Seles's former coach Michael Sell for the 2013 season.

"I had a great run with Craig, learned a lot and felt like I improved every year," said Isner. "I just felt like it was time for a different voice.

"[Craig] and I will remain great friends and he will always be someone I can go to for help or advice."

Isner, ranked world number 14, won two ATP titles last season.