Kei Nishikori took over four hours to battle his way into his first US Open quarter-final by securing a 4-6 7-6(4) 6-7(6) 7-5 6-4 victory over Milos Raonic.

Raonic delivered the first blow by taking a break point in the fourth game of the opening set, but Nishikori responded as the set progressed by breaking back.

However, Raonic was able to shake off the setback to break his opponent in a vital game to win the set and take the lead in New York.

Nishikori came out fighting in the second set and was able to earn a break at the first time of asking, but Raonic responded immediately by taking a break of his own to keep games level.

Both players secured another break apiece, which resulted in the tight contest being decided with a tie-break, which Nishikori was able to clinch 7-4 to get a set on the board.

Nishikori had eight break-point opportunities in the sixth game of the third set, and while Raonic struggled to create any chances himself, the Canadian was able to hold firm on his serve and eventually take a 2-1 lead by winning the tie-break 8-6.

It continued to be a close contest in the fourth set with games going by the way of serve, and neither player could muster a break point until Nishikori struck in the 11th game to push on and draw level on two sets all.

Games went by the way of serve in the early stages of the fifth and final set, but the momentum swung in Nishikori's favour when he sealed a crucial break point and was able to immediately hold his serve.

The 24-year-old continued to dominate and came close to another break, but Raonic dug in to save two break points.

With just one game left to win the match, Nishikori had only missed three shots in the fifth set when he stood with one game left to win to seal the match, but Raonic was able to hold his serve and extend the contest.

However, it didn't take long for Nishikori to serve his way to set up a clash against Stanislas Wawrinka in the final eight of the Grand Slam.