Dominika Cibulkova claimed the biggest victory of her career with a 6-3 6-4 win over world number one Angelique Kerber in the decider of the WTA Finals in Singapore.
Making her debut at the season-ending event, she raced into a 3-0 first-set lead, wrapping it up in 30 minutes.
The Slovak, 27, kept up the momentum and sealed an emotional victory with a dramatic double net-cord.
"This is the biggest moment of my career," said the world number eight.
She had lost to Kerber in the round-robin phase and booked her place in the final after a thrilling three-set win over Svetlana Kuznetsova of Russia on Saturday.
And she once again showed her determination and commitment against the German, who won two Grand Slams this year in Australia and the United States.
Cibulkova found her range from the start of the match, hitting winners at will and Kerber struggled to cope with the variety of shots.
The only time Cibulkova looked nervous in the 76-minute match was when she was serving for it at 6-3 5-4. She missed on three match points and saved two break points before winning.
Cibulkova, who will end the year as world number five, is the second player in a row after Agnieszka Radwanska to win the WTA Finals after only one victory in the three round-robin games.