Hours after winning his fourth Australian Open, he was on a plane heading toward Belgium, where he and his teammates swept the first three matches to clinch victory on indoor clay in Charleroi.

Unlike Wawrinka, whose three matches in Geneva required nearly 12 hours to complete, Djokovic had to play only one match: defeating Olivier Rochus in three straightforward sets. But he will presumably have to do much more than that if Serbia is to beat the United States on the road in the quarterfinals in early April.

That match will be played indoors in Boise, Idaho, on the campus of Boise State University at an altitude of about 800 meters, or 2,700 feet, which should make for quick conditions for the Americans’ big-serving singles players: Isner and Sam Querrey.

“If you want to lift the trophy, you need to beat the best teams, and that certainly is one of them,” Jim Courier, the United States captain, said of Serbia. “We know it will be difficult. But Boise should be a very hospitable environment for us. We’ll like the altitude there.”

Then again Isner, if he is indeed selected, generally prefers more time to get his long limbs organized. Then again, nobody plays better on a hard court in general than Djokovic. The Serb also would not have to suffer much jet lag to take part. The quarterfinals will come the week after the traditional American hard-court swing in Indian Wells, Calif., and Miami. But considering Djokovic’s chances of going deep in both those tournaments, he may not be at his freshest.

In the other quarterfinals, Argentina will play host to France on outdoor clay in Buenos Aires, and Kazakhstan and its naturalized Russian players will play host to the reigning champion Czechs. In a surprise matchup, Canada will play host to Italy, presumably on the quickest surface available in order to make the most of the huge serve and quick-strike instincts of Milos Raonic.

This is the first time Canada has advanced past the first round of Davis Cup’s World Group, but with Raonic winning the decisive match, it finished off Spain on Sunday. It was a major upset in terms of recent achievement — Spain has won the cup 5 times in the last 13 seasons — but no upset at all considering who actually took part.