Mueller dominated and controlled the pace of the game so far in a high-tempo attacking performance which immediately pulled fourth-seeded Gawad out of his comfort zone.

The world number 27 was on the cusp of a straight sets victory before the Egyptian fought-back to eventually force a decider inside the iconic Grand Central Terminal.

It was Mueller who eventually prevailed, though, winning 11-6, 11-6, 11-13, 3-11, 11-9 to reach the quarter-finals.

"I’m really over the moon," he said,

"That’s one of best matches that I have played in a long time and it is one of the biggest wins of my career.

"To knock out the defending champion here in New York, inside Grand Central, is pretty special."

England's Nick Matthew, the winner in 2012, beat long-term domestic rival James Willstrop to avenge his defeat to the same player last year.

The sixth seed won 11-8, 8-11, 11-8, 11-6 in a high-quality four-set encounter.

World number one Gregory Gaultier of France thrashed English qualifier Tom Richards 11-4, 11-5, 11-5 to set-up a quarter-final with Matthew.

Germany's Simon Rösner completed an all-European quarter-final line-up in the top-half of the draw by beating Egypt's Marwan ElShorbagy 8-11, 11-8, 4-11, 15-13, 12-10 in another encounter which went the distance.

Olivia Blatchford provided the home highlight as women's main draw action began by beating Hong Kong's Liu Tsz-Ling 11-5, 11-5, 11-9.

Top seed Nour El Sherbini of Egypt also began well by dispatching another Hong Kong player in Joey Chan, 11-5, 11-6, 11-8.