John Isner has parted ways with longtime coach Craig Boynton and has hired veteran U.S. coach Michael Sell, the New York Timesreports.

Boynton served as Isner’s coach since March 2009 and took him to a career-high No. 9 ranking in April 2012. The 27-year-old ended the year ranked No. 14, but was displeased with his Grand Slam results, losing four five-setters at the majors this season. After losing in the third round of the U.S. Open to Philipp Kohlschreiber, Isner went 2-5 during the fall swing.  
Sell first made his mark as the coach of Monica Seles, and in the fall of 2011, while working for the USTA, he helped Donald Young to reach his first ever ATP final in Thailand and end the year ranked No. 39.  
“I had a great run with Craig, learned a lot and felt like I improved every year,” Isner told the <em>Times</em>. “I just felt like it was time for a different voice. CB and I will remain great friends and he will always be someone I can go to for help or advice.”