Naomi Broady pulled off the biggest win of her career as she knocked Ana Ivanovic out of the ASB Classic in Auckland.
Ranked No.122 in the world, qualifier Broady beat the former French Open champion 7-5, 6-4 in 88 minutes to record her maiden victory over a top-20 player.
Ivanovic was the second high-profile player to exit on Tuesday after defending champion Venus Williams was knocked out by an 18-year-old wild card entry.
World No.16 Ivanovic, whose career earnings dwarfed her opponent's by £9.5 million ($14m), had no answer to Broady's service game.
The 25-year-old won 74 per cent of her first-serve points, notched 14 aces and didn't double fault once as she ousted the tournament's 2014 champion Ivanovic.
Broady's previous best came against world No.76 Jarmila Wolfe, last summer, and her reward this time was a tie with Latvia's Jelena Ostapenko in the second round.
The Ivanovic victory added gloss to a bright start to 2016 after Broady also beat qualifying top seed Magdalena Rybarikova 6-3, 1-6, 7-6(6) to secure a place in the main draw.
First Top 20 win!
@NaomiBroady blasts 14 aces to knock out 2014 @ASB_Classic champ Ivanovic 7-5, 6-4! #WTA pic.twitter.com/dtSQ6S5H34
— WTA (@WTA) January 5, 2016Broady has previously played predominantly in International Tennis Federation (ITF) tournaments rather than on the WTA's main circuit and came to prominence in the UK in controversial circumstances.
She had her funding withdrawn by the Lawn Tennis Association (LTA) as a teenager in 2007 after pictures of her on a night out appeared on social media.
Her brother Liam's decision to accept LTA funding and coaching several years ago then caused a family feud and father Simon continues to boycott the national body because of Naomi's funding cut.
Elsewhere, Caroline Wozniacki survived a day of top-seed exits after coming back from 4-0 down in the first set to beat Danka Kovinic 6-4, 6-4.
"It wasn't a great start for me, but a good start for her. I just had to get my wheels going and then I won seven games in a row, and I really felt like it was getting there," Wozniacki is quoted as saying by the WTA's official website.
"It's always tough in the first match of the season. You just want to get a good start and get the matches going. Honestly I was just trying to find my rhythm. She went for every shot and I wasn't keeping up."
At the Shenzhen Open, there was disappointment for Broady's fellow Brit Johanna Konta.
The British No.1 -- on the back of the best season of her career -- lost 6-3, 3-6, 6-3 to Chinese qualifier Qiang Wang little under two hours.
Konta, the world No.48, returned better numbers than her opponent -- the world No.110 -- on serve, but lost four of the five break points she offered up.