London
Less than a month ago, Samsonova was still looking to break into the top 100 in the rankings while trying to qualify for the Berlin grasscourt event.
The 22-year-old racked up seven straight wins to win her maiden WTA title in the German capital, becoming the first qualifier to win a WTA 500 event since Tsvetana Pironkova won Sydney in 2014.
Samsonova's strong serve and thunderous baseline hitting was once again on display on Court One as she broke Stephens' serve three times to claim the opening set.
Stephens, chasing a second week appearance at the All England Club for the first time since 2013, fought back with some brilliant court coverage and counter-punching but once again fell behind early in the final set.
Samsonova held her nerve and saved a crucial break point in the eighth game to maintain her slim lead, before sealing victory by sending down her fourth ace of the match.
"I want to thank the tournament organisers for this opportunity," said world number 65 Samsonova, who will next face eighth seed Karolina Pliskova for a place in the quarter-finals.
"I don't have the words to describe, I'm so happy."
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