David Goffin shocks Roger Federer, Grigor Dimitrov beats Jack Sock

Federer upset in final match of 2017 (0:47)

David Goffin rallies to beat Roger Federer 2-6, 6-3, 6-4 and reach the ATP Finals in London. (0:47)

LONDON -- Ahead of Saturday's ATP Finals semifinal, David Goffin said that he would "try something, something different, something that I've never done in the past" in an attempt to try to overhaul Roger Federer.

And against all odds, Goffin stormed from a set down to claim an impressive 2-6, 6-3, 6-4 victory to reach Sunday's final.

When asked in his on-court interview what he had changed in order to claim his first ever win over Federer, Goffin said: "Honestly I don't know. It was just the feeling. I was a bit nervous at the beginning, but I did some great serves, I was really aggressive so yeah, that was my day."

Federer, as the 14-time semifinalist against Goffin making his semifinal debut, was the one playing with everything to lose.

The Belgian opened the match well, acing Federer twice, but he threw away a game point allowing his opponent to swoop in and claim the first game with ease. Goffin was certainly displaying a more attacking performance than in his previous matches -- pelting balls into either corner and mixing the game up with sliced drop shots.

Federer made two wrong challenges within the first four games and there was a glimmer of upset.

But 22 minutes in and the world No. 2 held a comfortable 4-1 lead. Goffin -- after a solid performance against Dominic Thiem -- was attempting to move Federer, 36, around the court, trying to beat his opponent on consistency. Alas, Federer countered with deep crosscourt angles and stepped in to punish when many of Goffin's balls fell short of the baseline.

Eleven minutes later and a line-grazing ace down the middle closed the first set 6-2, easily in Federer's favour.

Still, Goffin wasn't about to give up on his finals hopes. He opened the second set with fight; holding another impressive service game before breaking Federer and then holding his second service game to love. At 3-0 in the second set, Goffin was digging his heels into the game.

Play continued with serve, but the early break allowed Goffin to serve for and claim the second set 6-3. Cheers of support for the underdog were soon muted by the hollers of "come on Roger!" at the beginning of the third set.

A double fault from Goffin at game point at 2-1 looked to have cost Goffin, but he turned it back around to lead 3-1.

This was certainly a different Goffin; forcing Federer to counterattack with attack. By 4-3 to Goffin in the third, the match looked as though it could go either way. A hold from Goffin and a hold from Federer and the Belgian was serving for the match.

"I have no words I cannot describe how I'm feeling, so much joy, so much happiness. Against Roger, it was such a special moment, I cannot describe," Goffin said after the match.

Goffin will face Grigor Dimitrov after the 26-year-old fought to a three set 4-6, 6-0, 6-3 victory over Jack Sock in the Pete Sampras semifinal.

Dimitrov had been on remarkable form throughout the tournament -- having won all of his Round Robin matches and having dropped just four games in his previous two -- but Sock was approaching Saturday's semifinal having won ¾ of their previous encounters.

Both players stepped out onto court with an air of confidence, but it was Dimitrov who took the early lead, breaking Sock in the second, much to the young American's visible frustration. A fiery next service game and Sock had made it onto the scoreboard at 3-1.

"I think in the beginning, I think I started the match exactly the way I wanted it. I think I just, after that break, that breakpoint at 3-0 in the first set, I think was a little bit of a turning point I felt for him. He stepped in the court, started being a little more aggressive. I let him play his game. I think that was the first set," Dimitrov said in his postmatch press conference.

Sock had found his momentum again and two games later and the scores were even once more. The mistakes were starting to creep in as Sock pushed Dimitrov hard on the attack; forcing him wide off the court and then forcing a sprint with a slice drop shot.

By now, Sock had won more games than Dimitrov had relinquished in his previous two games combined. It was turning into quite the contest. A crucial break for Sock in the ninth and the American found himself serving for the first set.

Sock had an 80% record on service games won coming into this match and he attacked this game with no less muster and sealed the first set 6-4.

In a familiar sequence, the second set started with an early break from Dimitrov allowing the 26-year-old Bulgarian a 3-0 lead. But this time, instead of seeing a fiery Sock comeback, Dimitrov stormed to a 6-0 second set victory, losing just nine points.

But this momentary lack of momentum didn't deter Sock's fighting spirit heading into the third. And what an incredible set of tennis the fans were gifted with as a result; drops shots, volleys and ace aplenty. A gruelling contest, but Dimitrov eventually crunched a final deciding set 6-3 victory.

On his previous encounter with Goffin earlier this week, Dimitrov said: "I wish I could just press 'replay'. I'm sure neither one of us is going to think about that. He's a very intelligent player. Knows his way around the court very well. Any given day, any particular moments, he makes it dangerous".