Jack Sock pulled out all the tricks, including a cunning "fake and bake" against Filip Krajinovic, to win the Paris Masters and a place in the ATP Finals.
The American will start a rank outsider for the season-ending event in London after clinching the last spot in the eight-man field headed by superstar veterans Rafael Nadal and Roger Federer.
World No.22 Sock qualified with a 5-7 6-4 6-1 win over Serbian Krajinovic in the Paris Masters final on Sunday.
The American's mixture of flamboyant baseline winners and court craft proved too much for the world No.77 to handle in the French capital.
At one set down and 5-4 up in the second, Sock completely outfoxed the Serb, before going on to level the match at a set apiece.
The American came into the net off the back of a tame backhand slice but his body language gave the false indication that he'd given up on the point.
However, just before Krajinovic hit the passing shot, Sock sprang back up in anticipation and volleyed the Serb's shot back over for a winner.
Sock, who started the week in 24th position in the Race to London, needed to win the Paris title to leapfrog Spain's Pablo Carreno Busta.
He wore down the defence of world No.77 Krajinovic, becoming the first American to win the title since Andre Agassi in 1999.
"There have been a lot of firsts. It started at the French Open with my first fourth round of a Slam, now I've won my first Masters 1000 in Paris," Sock said.
"This will be my first time in the top 10 and this will be the first time making the year-end Finals."
He is the first American man to make it into the singles draw of the elite season-finale since Mardy Fish in 2011.
"I obviously snuck into ... London unexpectedly so zero pressure on me to go there," Sock said.
"I'm going to swing big and play my game, like I always do, and just honestly enjoy the moment."
He is the sole player outside the top-10 to reach the London tournament from November 12-19, which is looming as a showdown between world No.1 Nadal and No.2 Federer, who split this year's grand slam titles two apiece.
Wimbledon finalist Marin Cilic and world No.4 debutant Alexander Zverev will also provide stiff competition at The O2.
However the slog of the long tennis season has taken its toll with some notable absentees.
World No.7 Novak Djokovic, a four-time winner of the tour finale, remains sidelined after ending his season in July to treat an elbow injury.
Third-ranked Andy Murray and Swiss star Stan Wawrinka are the other top-10 players to sit out, with their seasons cruelled by hip and knee injuries respectively.