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Fresh off his first round victory over India's Yuki Bhambri, Ebden continued his winning ways by taking down the world number 39 in 72 minutes.
Ebden got off to a flying start after breaking Millman's serve in the third game. He then served for the set at 5-4 and held his nerve to deny Millman the opportunity to break back by closing out the first set 6-4 in 41 minutes.
The world number 316 again broke Millman's serve in the first game of the second set before racing to a 4-0 lead.
He put pressure on Millman's serve at 5-1 and completed the tournament's upset after a back-to-back double fault by his compatriot ended the contest.
"It's never easy to play each other but I'm really glad I executed a good game plan. May the best man win and I'm really happy that man was me today," Ebden said.
France's Adrian Mannarino lived up to his top seed billing and looks forward to seeing the return of fans after defeating Italy's Roberto Marcora 6-3, 7-5.
"It's just a little bit sad to play in an empty court like this. It feels like you are playing a practice match at 7am ... and everyone's sleeping," Mannarino said. "So it's very nice to know that the fans are coming back this weekend."
Moldova's Radu Albot beat Germany's Yannick Hanfmann 6-7 (2/7), 7-6 (9/7), 6-3 while South Korea's Soonwoo Kwon also advanced after a 6-3, 6-4 win over Japan’s Yasutaka Uchiyama in the day's other singles matches.
The players have been playing to an empty gallery during the week because of coronavirus restrictions, but organisers said that up to 250 fans a day will be allowed to watch the weekend's semi-finals and finals in person.
All spectators must take a mandatory Covid-19 test and will only be allowed into the venue if their result is negative. They must wear masks at all times and will not be allowed to mingle between groups.