Halloween evokes humor in Novak Djokovic, who has celebrated past holidays by striding on court dressed as The Joker and Darth Vader. But staring down John Isner's monster serve and a one-set deficit today, Djokovic was in no mood for masquerades.

Reading Isner's serve with scrutiny and striking low returns with authority, Djokovic broke four times in the final two sets to dismantle the towering American, 6-7 (5), 6-1, 6-2, earning his 14th consecutive win and set up a compelling Paris Masters quarterfinal with Stanislas Wawrinka.

Today's clash centered on a stroke conflict—How would ATP ace-leader Isner's explosive serve stand up to Djokovic's sniper return?—and an emotional issue: Could Djokovic, who dissolved in a 7-6 (5), 3-6, 7-5 quarterfinal loss to Isner in Cincinnati two months ago, keep his cool amid the swirling frustration and fear that can unsettle like a 140 M.P.H. blast into the body? Djokovic delivered plenty of answers.

The 2009 Paris champion earned five break points in Isner's first two service games, but the American slammed down his fourth ace to deny Djokovic's fifth chance, eventually holding for 2-1. Serving almost exclusively wide to Isner's forehand on the deuce side, Djokovic spread the court effectively, exploiting the bigger man's issues in changing direction and making the necessary rapid-recovery steps. Djokovic held at love three times in the first set, drilling an ace wide to force a tiebreaker.

The freak factor spiked considerably in the tiebreaker, as Isner went up two mini-breaks only to see both dissipate as a full-stretch Djokovic forehand return hit the tape and dribbled over for 2-3. Undetered, Isner swiped a massive inside-out forehand followed by a hellacious kicker to give him triple set point. On his third, Isner erupted with a 139 M.P.H. ace, only to see it wiped out on a let-cord call. But the world No. 16 imposed his lethal serve-forehand combination to take the first set on the strength of 20 winners—and all six break points he saved.

Facing Isner's outrageously oversized serve can feel like waking up in your house and finding all your mirrors replaced with funhouse mirrors: The dimensions of the space haven't changed, but everything looks absurdly distorted. Djokovic began stepping in closer to take some returns on the rise and challenged Isner with dipping returns back at his feet. It worked: Isner won 72 percent of his first-serve points in the opening set, but barely won 50 percent of first-serve points in the final two sets.

Denied on his first seven break points, Djokovic was hardly spooked. He took charge on the eighth, coming forward, and when a weary Isner slapped his backhand pass into the net, Djokovic celebrated the break and a 3-1 lead raising his arms in a physical expression of "Finally!" The second seed backed up the break with a love hold sealed by an ace, winning 12 of the prior 13 points to build a 4-1 lead. Blasting back a return right at Isner's feet, Djokovic converted his seventh break point of the second set for a 5-1 lead and closed the 25-minute second set with a love hold.

Djokovic, who won 17 of 19 trips to net, continued to press the issue, breaking with a sharp inside-out forehand for a 3-2 lead in the decider. Approaching behind a low backhand slice, he drew an Isner error to break for 5-2 and closed with a slick serve-and-volley combo. Djokovic has won 13 of 15 meetings with Wawrinka, but the last two have been five-set epics in Melbourne and Flushing Meadows earlier this season.