ATP World Tour Finals: Wawrinka beats Ferrer, waits for Nadal favour
But Switzerland's first-time participant in the year-end event will, however, need a victory from Rafael Nadal in a later concluding Group A match over Tomas Berdych.
A Nadal loss would give Berdych a spot in the final four alongside the Spanish world number one. Wawrinka was pleased with his battling effort against Ferrer in just over two and a quarter hours after throwing away the first set while leading 5-2 but losing in a tiebreaker.
"Sure, tonight I will be a big fan of Rafa," said the winner. "I did my job all the week, did the best I could for all three matches. "I'll watch and see what happens. Of course I'll be happy if Rafa wins." Wawrinka committed a massive 30 unforced errors in the 61-minute first set against the 31-year-old Ferrer.
Even if the Spaniard had nothing to lose, and was out of semi-final contention, he fought like a terrier to keep Wawrinka off-balance in the first set. Ferrer rallied from the depths, breaking in the ninth game and again in the 11th for 6-5 after the Swiss saved four break points.
But a break-back from Wawrinka levelled at six apiece to bring on the decider. Ferrer sprinted to 3-1 and eventually took the set to Wawrinka's dismay from a Swiss forehand error. Wawrinka came back in the second with an early break which was enough to see him through to one set each.
In the third set, the Swiss sensed the finishing line and earned two breaks to bolt home after conversions on six of seven break points. He struck 35 winners and overcame 56 unforced errors. "What can I say, I'm so happy right now," said Wawrinka, who ended 2-1 in group play.
"David is so tough and playing so well. I had to fight so much to get the win, but I'm really, really happy. This was so important for me. "This is my first finals and I had a tough match, I had to focus on my tennis and that was the most important thing."
Nadal takes a 16-3 record over Berdych into their match, having won the pair's last 15 meetings.