India’s Prajnesh Gunneswaran earned a morale-boosting win over former world No 8 Jack Sock to reach the quarter-finals of the Atlantic Tire Championships, an ATP Challenger in Cary, USA, on Thursday night.

The left-hander notched a 6-7(3), 6-2, 7-6(5) win over the American after a tough battle that lasted just seconds short of three hours, celebrating his 31st birthday in style. He clinched the decider in a tiebreaker, fighting back after the former Paris Masters champion took the first set.

In a tight match, Prajnesh converted three of the 12 break points he got but lost his serve just once and gave away only 3 break chances himself. He kept his serve steady with 73% of first serve points won and held his nerve in the final tiebreaker.

Seeded fourth, the world No 146 will play Brazil’s Thomaz Bellucci for a place in the semi-finals.

Sock, a former Top-10 player who has won a Masters title and played the ATP Finals, is down to world No 253 in the singles ranking.

Prajnesh had beaten Canadian Peter Polansky 6-2, 6-2 in his first match and is the only Indian in contention after Ramkumar Ramanathan bowed out.