Breaks of 93 and 70 helped Gould establish an early 2-0 lead, but Maguire – aided by a tremendous 145 – reeled off three frames on the bounce to sneak ahead.
The pair then shared the next two frames to leave world number 14 Maguire with a 4-3 advantage before Gould drew level with a timely 62.
It was world number 30 Gould who clinched the decider, potting the final black to clinch the ninth frame 65-57.
"I felt really good the whole way through," said Gould. "I'm not used to being in the latter stages of ranking events so it's going to be a whole new experience for me tomorrow.
"I'm looking forward to it and hopefully I can keep playing the same way.
"It's a very good start to the season. I've worked hard for a few months to get my game back on track."
Gould will next face Joe Perry, who bagged a 137 break en route to a 5-2 victory over Robin Hull.
The other semi-final will pit Neil Robertson against Barry Hawkins after the duo ousted Shaun Murphy and Marco Fu respectively.
Wuxi Classic - Quarter final results
Neil Robertson 5-4 Shaun Murphy
Barry Hawkins 5-4 Marco Fu
Martin Gould 5-4 Stephen Maguire
Joe Perry 5-2 Robin Hull