Andy Murray pushed British number two Kyle Edmund all the way on Wednesday but eventually went down 6-7 (2-7) 7-6 (7-5) 10-5 in the Battle of the Brits.
Murray won his opening singles match at the six-day charity event – organised by his brother Jamie – against Liam Broady on Tuesday.
But despite taking the opener at the National Tennis Centre in Roehampton, the former world number one was unable to make it two victories from two.
Instead, it was Edmund, who defeated James Ward in his opening match, who secured his place in the semi-finals when Murray looped a backhand return out of play.
"Finding a way really, getting through it. It wasn't like I was down [in breaks] but I was down after the first set," Edmund told Amazon Prime following his triumph.
"Then there was a period where it was scrappy a bit, a few errors from me and you could tell he was slowly building.
"I just told myself to hang in and give myself a chance. He just puts balls in the court, he has very good anticipation, uses the area of the court very well, uses different speeds.
"Everyone wants to win and do their best. You are still playing Andy Murray, a guy who has won so much."
Despite his defeat, Murray can still make the semi-finals should he overcome Ward in his next outing.