Their 46th meeting. Their first since 2016.
Two of the greatest rivals ever seen in tennis will go toe-to-toe in Cincinnati, with a potentially historic win on the horizon.
Djokovic is a five-time runner-up at the Western & Southern Open, losing to Federer on three occasions and Andy Murray in the other two finals.
Remarkably, if he records a win on Sunday, he will become the first man to win all Masters 1000 titles.
Federer, who is short of one Masters title himself – in Monte-Carlo, where hes unlikely to play anytime soon never mind win – can level his head-to-head with the Serb to 23-23 should he record the win.
The 37-year-old Swiss already holds the record for the most titles secured at this event – and no doubt he would be delighted to extend that record on Sunday against a familiar foe.
Since 2015, they have met in seven finals, Djokovic won five of those. However, the landscapes have shifted somewhat since their last meeting.
Then, Djokovic dominated Federer to reach the Australian Open final as he picked up the third Grand Slam title on his way to holding all four majors.
A dip in form and elbow injury saw Djokovic pushed to the back of the queue as Federer and Rafael Nadal split six Slams between them in a year-and-a-half from 2017.
Federer won three majors in that time and will now stand between Djokovic and an exciting piece of history.
The duo have met three times on this battle ground, all in the final – Federer has never lost this match-up.
Djokovic comes into this match full of confidence. He ended his two-year wait for a major at Wimbledon and although he wasnt on top form earlier in the week, hes picked up some impressive wins over Grigor Dimitrov, Milos Raonic and Marin Cilic.
Route to Cincinnati final
R2: 6-4 6-4 Gojowczyk
R3: 6-2 7-6 Mayer
QF: 6-7 7-6 6-2 Wawrinka
SF: 7-6 1-1 RET Goffin
R1: 6-4 7-6 Johnson
R2: 4-6 6-2 6-1 Mannrino
R3: 2-6 6-3 6-4 Dimitrov
QF: 7-5 4-6 6-3 Raonic
SF: 6-4 3-6 6-3 Cilic
David Goffin – Federers semi-final opponent – was forced to retire in the semis, while Federer defeated his compatriot, and the ever-improving, Stan Wawrinka in the quarter-finals.
Now they head for a beautiful match-up. A clash of styles. Weapons that can hurt one another. Both mentally prepared for serious warfare.
Federer may perhaps feel he has a point to prove. He hasnt faced the Serb since his triumphant return from injury – the chance to exude dominance over the current world No. 10 must be tempting.
For both, its a chance to score a mental point ahead of the US Open.
The pair, along with Rafael Nadal, will no doubt enter the event as the favourites.
Of the seven finals reached at Flushing Meadows, Djokovic has only won two titles. Federer is without a victory since 2008 – a 10-year gap. Both have scores to settle.
Djokovic said on facing Federer: We havent played each other for quite some time, which is unusual, because Im used to playing Roger, over the course of almost 10 years, I have played him so many times. Played him the most after the rivalry with Nadal.
He has influenced greatly – the rivalry with him and him personally has influenced the evolution of my game. So, I mean, it would be the greatest challenge in Cincinnati, without a doubt, and many tournaments, especially here, because hes been dominating this tournament historically. He won against me several times in finals.
You know, obviously he feels great in these conditions and this surface. But, you know, obviously he has to win his semifinals, and well see what happens tomorrow.
Federer added: Its like fresh, you know. Its not like we have played in the last few weeks and everybody knows what to expect.
I mean, we know how we could look like, but were not quite sure, the fans, you guys, us, as well, to be honest.
A lot has happened since, you know, with injuries both of us have been fighting, and we both came back strong again. So I think thats whats nice about this time around with Novak in the match.
Its nearly an impossible tie to call – as ever with these great champions – but I do slightly favour Federer, who the conditions may suit a little better.
Prediction: Federer in 3