He won a total of only three matches at Grand Slam tournaments all year, making it as far as the third round just once and bowing out in the opening round twice. During one particularly rough stretch from August to early October, he lost five times in a row.
The 25-year-old American turned things around at the end of the season, so much so that he ended up earning a debut appearance at the ATP Finals, starting with a match against 19-time major champion Roger Federer on Sunday in London.
"It's hard when you have a bit of a period where it doesn't go as well as you would like.