MELBOURNE—A Fortune 500 CFO once said that numbers are way to explain a series of relationships. This evening’s Australian Open semifinal between defending champion Novak Djokovic and Roger Federer featured enough quantitative data to conduct a massive group therapy session.

Between them, these two had won 13 of the last 16 Australian Opens—seven for Djokovic, six for Federer. But in the end, Djokovic’s 7-6 (1), 6-4, 6-3 win proved that when it comes to the majors over the last seven-plus years, he seems to have Federer’s number.

Prior to this match, Djokovic had beaten Federer five straight times at a major, the Serb’s last defeat coming in the semis of Wimbledon in 2012.

This was the 50th time the two had played, Djokovic leading the rivalry 26-23. Pointedly, of Federer’s 23 wins, only one had come after he’d lost the first set (2014 Dubai, semifinals). This was exceptionally significant in the wake of the groin injury Federer had suffered during his quarterfinal win over Tennys Sandgren two days ago. Everyone was aware that the first set was paramount for Federer.

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Djokovic adds more Australian Open numbers as an ailing Federer wilts

Djokovic adds more Australian Open numbers as an ailing Federer wilts

Federer’s injury was apparent, but the indeterminate nature of its extent made him dangerous and mysterious. Djokovic was puzzled. Play self-contained, steady tennis? Or charge hard and seek to blow Federer off the court?

As Djokovic hesitated, Federer couldn’t help but fill the vacuum, particularly given a number he shared after the match: three, as in the three percent chance he gave himself of winning.

Variety, opportunism, precision. These were Federer’s three watchwords as the match began. Except on his serve—eight aces in the first set—power took a back seat to placement. With Djokovic serving at 0-1, 15-40, Federer snapped open a rally with a drop shot, lured Djokovic forward and drove a backhand passing shot winner up-the-line.

“I was playing with nothing to lose obviously,” said Federer. “I was just trying to take big cuts at the ball, trying to keep the rallies to a minimal, make sure I keep him off guard, mix it up as much as I can.”

At 1-4, Djokovic looked listless. A long backhand at love-30 put him in a major hole.

“When I was on the court at the beginning,” said Djokovic, “I was really paying too much attention on his movement, what he was really doing. I wasn't in the right balance. I wasn't hitting the ball. I wasn't executing the shots the way I wanted it.”

Djokovic adds more Australian Open numbers as an ailing Federer wilts

Djokovic adds more Australian Open numbers as an ailing Federer wilts

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There followed a Djokovic service winner, an ace (earned on a challenge) and a netted Federer forehand. From deuce, Djokovic held. Three games later, Federer served for the set at 5-3 and was broken at love.

The subsequent tiebreaker was all Novak, the Serb playing the same brand of error-free tennis that had helped him win three tiebreakers in last year’s Wimbledon final. Also aiding Djokovic was his improved serve, as FiveThirtyEight.com explained.

As Djokovic became airtight and assertive on this hot, sticky, windless evening, the air went out of Federer’s balloon, vividly demonstrated when he took a medical timeout after the first set.

In the first set, despite winning only 23 of 57 baseline points, Federer had snapped off 26 winners. Life got far more sober for Federer in the next two sets: 8 winners in the second set, 12 in the third. And then there was this number: in the second set, Federer won a mere five of 22 baseline rallies.

“Today was horrible,” said Federer, who at last could take some pride in still having never retired mid-match once in his entire career.

Djokovic adds more Australian Open numbers as an ailing Federer wilts

Djokovic adds more Australian Open numbers as an ailing Federer wilts

We have become spoiled by Roger Federer’s longevity. To have reached another Grand Slam semifinal at the age of 38 is a remarkable achievement.

“At the end of the day I guess I'm very happy," he said. "I got to be happy with what I achieved. It was the maximum to go to get at this tournament, especially after the Millman and the Sandgren match.”

But it has become increasingly clear in recent years that the brilliant Swiss must continue to schedule himself prudently, minimize long points and maintain the elegant level of execution that has made him the most swooned-over player in tennis history.So great is Federer that even seeing him in decline compels.

Djokovic is now 8-0 in Australian Open semifinals. In large part, this tournament is as much his personal playhouse as Roland Garros is Rafael Nadal’s. Djokovic’s final-round opponent will be the winner of tomorrow’s semi between Dominic Thiem and Alexander Zverev.

Assessing Thiem, who has won four of their ten matches, Djokovic said, “It seems like he's improved his game a lot on hard courts, because his game is more suitable to the slower surfaces. The clay of course being his favorite surface.  But winning Indian Wells I think last year, beating Roger in the finals, that probably gave him a lot of confidence that he can win big tournaments on other surfaces, as well.

"He definitely has the game. He has the experience now.He has the strength. He has all the means to really be there.”

As for Zverev (2-3 versus Djokovic): “It's impressive with the way he has been playing so far in this tournament, building his game, raising the level of tennis that he's been playing.”

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Djokovic adds more Australian Open numbers as an ailing Federer wilts

Djokovic adds more Australian Open numbers as an ailing Federer wilts

A win Sunday night will also yield two more numbers that would greatly please Djokovic: a return to the number one ranking, and Grand Slam title number 17.

So the CFO had a point about how numbers can articulate relationships. It had taken a while versus Federer, but Djokovic has liberated himself from the subordinate role and become the alpha male of this match. Having made 11 unforced errors in the first set, he committed just seven over the next two.

It was a grim task this evening, but Djokovic was able to at last complete it.

Djokovic adds more Australian Open numbers as an ailing Federer wilts

Djokovic adds more Australian Open numbers as an ailing Federer wilts