Juan Martin del Potro overcomes Ryan Harrison challenge at US Open

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.