Gilles Simon staged a dramatic comeback to knock out top seed Marin Cilic and set up the title clash with second seed Kevin Anderson, who prevailed over a spirited Benoit Paire at the Tata Open Maharashtra, in Pune on Friday.
In a sensational turnaround, the unseeded Frenchman toppled the world No. 6 from Croatia 1-6, 6-3, 6-2 in a gripping semi-final.
He had also sent third seed and defending champion Roberto Bautista Agut packing in the second round.
Simon, who was once a top-10 player but is now placed at a humble 89th, shrugged off the opening set debacle to stun Cilic, the 2017 Wimbledon finalist, in an hour and 51 minutes.
He will now gun for his 13th ATP title, having played his last final in September 2015 when he lost to compatriot Jo-Wilfred Tsonga at home in Metz.
Anderson, the US Open finalist, rallied to edge out Paire 6-7(6), 7-6(2), 6-1 in two hours and 19 minutes.
Cilic was ruthless in the beginning but Simon effortlessly changed the complexion of the game. From nowhere, he seized the momentum to rattle Cilic.
His consistent returns, even on the powerful serves of Cilic, unsettled the Croat, who started to make unforced errors and could never really recover.
Simon came to the match with a superior 4-1 head-to-head record against Cilic and maintained it. They last played in 2016 at the Miami Masters, where Simon won in a three-setter.
Simon endured a tough 2017 season during which he struggled to reach even quarter-finals on Tour and his ranking plummeted to 89 from 24 at the beginning of the year.
Once ranked world number six, Simon struggled to find his rhythm as his ground strokes were all over the place in the opening set.
Cilic, as usual, began in an explosive manner firing aces and service winners while Simon struggled to win points on his own serve.
The Frenchman dropped serve at love in the second game and won only two points in the first three games of the match, underlining the dominant start the Croat made.
After being broken at love, Simon saved two break chances in the fourth game but netted a backhand on the third while Cilic held his own to race to a commanding 5-0 lead.
Egged on by the crowd and aided by Cilic's unforced errors, Simon got on board by holding his serve in the sixth game in which he saved two set points.
Cilic though remained ruthless and began serving for the set with an 226km ace and closed it with another on his fourth set point.
In a complete turnaround, Simon started to return better in the second set.
The Frenchman began to hold his serve and broke Cilic in the second game to take a 3-0 lead in the second set. The break happened in a bizarre manner. At 30-30, Simon found a surprise service return winner as Cilic left the ball, thinking it was going out.
On the break point, the Croat netted a backhand. Simon broke Cilic again when his rival hit a backhand long on the second break point and found himself leading 4-0.
With momentum on his side, Simon began to dominate rallies as he stunned Cilic with some amazing winners and served out the set in the ninth game.
From 40-15, Cilic lost his serve in the opening game of the decider to hand the initiative to his opponent.
The next game was an engrossing battle with Simon fighting off two breakpoints after four deuces to hold his serve. Cilci had no clue how to cope with returns from Simon.
The Croat dropped serve at love in the seventh game and Simon served out the match when Cilic committed a backhand error on second match point.