The Croatian, ranked 55 places below Zverev, battled back from a set down and displayed tremendous self-belief through sets three and four to oust the 20-year-old German – backed by many to go all the way in Flushing Meadows.
Instead, Zverev flattered to deceive after the opening set in which he motored through in 26 minutes and dominated behind his big first serve. He never offered Coric a break point opportunity until the sixth game of the second set but his conviction seemed to unravel after the Croatian broke in the twelfth game of set two to level proceedings.
Rarely did Zverev exploit his opponent when offered break opportunities but Coric showed immense levels of confidence in set four when faced with frequent 0-30 deficits on his own deal.
The handshake from the German at the end told the story and he will depart New York having yet to get the Grand Slam monkey off his back. The German’s wait to reach the quarterfinals of a major goes on despite his glittering success on the ATP tour.
Coric, meanwhile, can look forward to a third round clash with Kevin Anderson.
Ebb and flow
Zverev could have hardly asked for a more pleasing start after his 2am conclusion on Tuesday morning and he raced through the gears in set one without offering Coric a sniff.
The break arrived in the sixth game after the Croatian uncorked on a forehand error and he would not relinquish the advantage. Coric, though, was otherwise convincing behind his own deal and it would bode well throughout the match.
The pair traded holds in the second set and nothing could separate them. Zverev salvaged a pair of break points behind his reliable serve while Coric was painting the lines with his rasping groundstrokes. A deft lob at 30-all in the ninth game appeared to edge the second set towards a tie-break but Coric revolted, outpowering Zverev on his second set point to level the match.
The match stayed on serve throughout the third set and neither player could grab the break opportunities presented. A 39-stroke rally at 3-3 denied the German a break opportunity and he sunk to the floor both out of disbelief and as an opportunity to catch his breath.
Grit and Steel
This time a tie-break was called into action and it was Coric who rose to the occasion, racing out to a 5-1 lead before the German double-faulted to allow his Croatian counterpart to close out it with an ace.
Zverev, it appeared, was embroiled in a battle with the Coric who prevailed in their only previous encounter two years ago and mentally he was left wanting in the decisive fourth set.
The first signs of pressure came in the sixth game when the Croatian held after a nine-minute service game and he was forced to hold from 0-30 in his very next service game. He was being spared by Zverev’s reluctance to come to the net and his back was against the wall when he found himself in a love-40 hole – and down three set points – at 5-6.
Instead, he came out better during another grueling exchange to force a tie-break and a single mini-break set the course. Match point was fashioned with a pulverizing smash before the world number six arrowed a forehand long.