Laver Cup Day 3 Blog: Federer, Isner and Sunday's dramatic finale

WATCH—Roger Federer on Laver Cup success and US Open shortcomings:

The third and final day of the Laver Cup is upon us, and while it was always going to matter—it is impossible to amass the 13 points needed to clinch the trophy over the first two days—it's shaping up to be quite dramatic.

Team Europe leads Team World by a 7-5 margin; you can read my analysis and watch video highlights of Day 1 play here, and Day 2 play here.

All of today's matches are worth three points each, and the lineups have been revealed. I'm a bit surprised Team World didn't elect to have Anderson play second in what could be a must-win match. But in this arrangement, Isner won't have to play—then stop for an extended period of time—and then play again. Still, captain John McEnroe runs the risk of not playing arguably its best singles player in a live match on the final day.

Team Europe is banking on Federer in the early going; he'll play twice in a row—and twice against Isner—before potentially giving way to Zverev, who would have to play, rest, and then play again.

Team Europe can clinch the Laver Cup by winning any two matches; Team World can clinch by winning any three. If the fourth and final match is required—which would happen if Team World wins two of the first three matches—it will come down to Kyrgios and Djokovic, who are a combined 0-2 in singles play in Chicago.

Stay tuned to this page for updates, analysis and highlights throughout the day.

It's hard to boil down a fast-moving, fast-paced doubles match to a single turning point, but not in this case. Trailing double match point in the 10-point match tiebreak with Isner returning serve—an ideal scenario for Team Europe—Team World needed an answer to avoid a 10-5 deficit in the Laver Cup and the prospect of needing to win all three remaining singles matches.

To the delight of the Chicago crowd—very much behind Sock and Isner, I thought—the 6'10" American provided one of the best possible answers after returning serve:

WATCH: Isner saves match point with remarkable forehand pass

"It was nasty," Sock said of his partner's heroics.

Even though it doesn't make much for a momentum swing in this particular match format, this outcome was still something of a surprise. Sock and Isner needed to win two consecutive tiebreaks, one standard and one 10-point, and twice surrendered mini breaks to Federer and Zverev in the latter. Federer was a force at net, to say nothing of the rest of his game, and while Team World picked on the young German whenever possible, Zverev came up with some remarkable volleys of his own.

Plus, Team Europe could just pick on Isner—right?

"I'm still out of breath," Sock said afterward. "Holy cow—I'll keep it PG—that was epic."

WATCH: Sock and Isner clinch dramatic doubles win for Team World

Isner and Sock won 92 percent of their first-serve points in the second set, holding games with incredible ease. But it was their play when the chips were down that was most impressive.

The outcome raises the stakes for the next match—against featuring Isner and Federer—and assures that Anderson will compete in singles play. He'll face Zverev, who will probably benefit from a cool-down session.

But how do Isner and Federer feel? That's the bigger question. This we know for sure: Isner is feeling good right now.

And so is Sock. Asked if Isner will beat Federer on the court again, the American kept it simple: "Hell yeah."

Federer led the first-set tiebreaker 4-1, and lost it. He got to 15-40 on Isner's serve at 3-3 in the second set, and lost the game. After saving a match point on his serve, Federer got to 0-30 on Isner's serve at 5-5—and lost the game.

So when Federer tried an ambitious swing volley not far from the baseline at 3-3 in the second-set tiebreaker, and saw that shot clip the tape and land wide, you had the feeling that the 20-time Grand Slam champion was about to pay for all his missed opportunities.

Those missed opportunities traveled the spectrum of the error scale—some cover-your-eyes unforced, some forced by his opponent's all-out aggression—and were also a result of Isner's powerful play. Isner's serves were landing, but so were his groundstrokes, even when out of position. All the big man needs to do is get a racquet on the ball, and it can explode off the strings. He even carried over some volleying skills from his successful doubles match earlier in the day.

Isner appeared to take full advantage of his opening when he stretched his 4-3 lead to 6-4—double match point.

And then, finally, Federer's previously dormant best surfaced. Watch the below highlight for the specifics, but Federer's third match point save—the second in this sequence—is to be seen to be believed:

WATCH: Federer saves two match points, forces match tiebreak

When Federer then took a 5-2 lead, with two serves, in the match tiebreak, all of his previous faults were seemingly forgotten. That is, until he dropped both service points, along the next two points, to inexplicably fall behind 6-5.

"That's all about John Isner's serve pressure," Tennis Channel's Paul Annacone said as it unfolded, and he would know—he was once Federer's coach.

But like he did in the second-set tiebreaker, Federer got a reprieve. After stabilizing by holding both service points, Federer regained a mini-break lead when Isner struck a forehand wide. Finally, the pressure looked to be getting to Isner, who had already lost one singles match in this Laver Cup despite holding a match point.

When Federer earned three match points at 9-6—after saving three match points in total—he soon completed a scratchy but ultimately successful win for Team Europe, which now needs just one more match win to retain the Laver Cup.

HIGHLIGHTS: Federer edges Isner, gets Team Europe to within one victory of Laver Cup

WATCH: Team Europe awarded the Laver Cup

The Laver Cup is staying with Team Europe. With a Cup-deciding match between Nick Kyrgios and Novak Djokovic looming, Zverev saved all five Anderson break points in the second set, pieced together an out-of-nowhere break to force a match tiebreaker, and was the better player in the most critical moments. The German won the last five points of the 10-point finale, while Anderson failed to put the ball in play in either of the final two points.

WATCH: Alexander Zverev clinches the Laver Cup for Team Europe

Stay tuned to TENNIS.com for more Laver Cup highlights, a report from Richard Evans in Chicago and thoughts from Steve Tignor in New York.