Djokovic, aiming to guide Serbia to their first title since 2010 and second overall, made light work of his opponent as he dropped just six points on serve and did not face a break point while claiming a 6-3 6-2 victory in under an hour.

"I felt very good. I was locked in from the first point, determined to execute the game plan," Djokovic told reporters.

"The crucial game was the eighth game of the first set, 4-3, new balls. I managed to put in a couple of extra returns, make him play, mix up the pace. After that, there was really no looking back. I just served well, moved great."

Lajovic had a much tougher time against Melzer, the younger brother of fellow professional Juergen, as he was forced to toil for a 7-6 (7-5) 3-6 7-5 win.

The 31-year-old squandered a break advantage in the third set but recovered to convert his fourth match point and seal victory.

"It is the Davis Cup. It is the emotions, the stress, the pressure. It is the tight moments all the time," said Lajovic. "He played some good tennis in the past couple of months, and had confidence and showed it today, playing great tennis.

Nikola Cacic and Filip Krajinovic made it a clean sweep for Serbia with a 7-6 (7-4) 4-6 6-3 win over Oliver Marach and Philipp Oswald.

Elsewhere, Lorenzo Sonego and Jannik Sinner secured emphatic wins in their singles rubbers to give Group E hosts Italy a 2-0 lead against the US in Turin before losing the doubles dead rubber in straight sets.

Debutant Sonego got the Italians off to the perfect start with a 6-3 7-6 (7-4) victory over big-serving Reilly Opelka with a disciplined display that included only one unforced error.

"It was not easy to play here, but this crowd ... It's the first time in Davis Cup and I was so looking forward to this match - thank you everyone," said the 26-year-old.

World No.10 Sinner, who made his debut at the season-ending ATP Finals this month, put the tie beyond doubt as he smashed 17 winners in a 6-2 6-0 thrashing of John Isner.

"Playing here was very special," Sinner said. "Today we have won already, which is great. We have a great team and everyone is a great guy as well, so we are just trying to stay together. I am very honoured to be a part of this."

In Madrid, Feliciano Lopez and Pablo Carreno Busta helped holders Spain to an insurmountable 2-0 lead over debutants Ecuador.

Veteran Lopez breezed past Roberto Quiroz 6-3 6-3 before Carreno Busta fought back from a set down to beat Emilio Gomez 5-7 6-3 7-6 (7-5) and secure victory for Spain.

Carreno Busta then returned for doubles action with Marcel Granollers and the Spanish duo earned a 6-4 6-7 (7-5) 7-6 (7-2) win over Gonzalo Escobar and Diego Hidalgo.

Australian Associated Press