London-born Ward turned professional in 2004
Britain's James Ward recorded the most famous win of his career when second seed Feliciano Lopez was forced to retire at the Eastbourne International.
It was only a second Tour-level victory for 23-year-old wildcard Ward, ranked 342 in the world, following a win in one round of this tournament in 2009.
He was leading 6-3 5-4 with two match points when Spaniard Lopez withdrew because of a shoulder complaint.
"I'm very happy, it's obviously the biggest win of my career," Ward said.
"I'm obviously disappointed that I didn't get the chance to finish. It looked like he was struggling. He's got Wimbledon coming up next week so he needs to be careful."
The British number five decided to play at Eastbourne in a bid to boost his ranking rather than attempt to qualify for Wimbledon.
"At the moment I'm not playing," he added. "I was offered the chance to play here and I decided it would be best for my ranking."
The Londoner will play Queen's semi-finalist Rainer Schuettler in the next round on the Sussex coast after the German defeated Kazakhstan's Andrey Golubev 6-2 6-3.