It took Juan Martin del Potro four sets to see off Ryan Harrison in the second round of the US Open at Flushing Meadows.
The Argentine looked on course for a routine victory after taking the opening two sets 6-2 6-3.
However, world number 61 Harrison saw the momentum swing his way in the third before taking the set 6-2.
The 2009 winner then saved two break points before breaking Harrison's serve twice to seal the win 6-2.
Del Potro will meet fellow countryman Leonardo Mayer in round three.
