MADRID (AFP, REUTERS) - Karen Khachanov and Andrey Rublev helped Russia open the inaugural Davis Cup Finals with a 3-0 victory over defending champions Croatia in Madrid on Monday (Nov 18).

World No. 17 Khachanov clinched the winning point in the Group B match by fighting back to beat Croatian No. 1 Borna Coric 6-7 (4-7), 6-4, 6-4, after Rublev had earlier seen off Borna Gojo 6-3, 6-3.

"When you're playing not only for yourself, but for your country, you have to fight harder," said Khachanov.

Later, Canada claimed a 2-1 victory over well-fancied Italy to strike first in Group F.

World No. 12 Fabio Fognini slumped to a 7-6 (7-5), 7-5 defeat by Vasek Pospisil, ranked 150th, before rising star Denis Shapovalov edged out Matteo Berrettini 7-6 (7-5), 6-7 (3-7), 7-6 (7-5).

"I'm really happy to get the win against a player like Matteo who has had such a good season," said Shapovalov. "I always love representing my country... It's not often you get to play as a team, so it's amazing."

Meanwhile, British team captain Leon Smith has said Andy Murray is a welcome addition to their team but there is no guarantee the former world No. 1 will play singles in their Group E ties against Kazakhstan and the Netherlands.

The 32-year-old, who underwent hip surgery in January, won the European Open in Antwerp last month but the three-time Grand Slam champion is the lowest-ranked singles player in his team at 126, behind Dan Evans (42) and Kyle Edmund (69).

"Any time you can bring Andy into the team is going to make your team better," Smith told reporters. "He's still working his way back to the level he wants to get to, so people have to keep the expectations of the right level of where he's at just now."

Russia, who are without US Open runner-up Daniil Medvedev owing to exhaustion, can wrap up a place in the quarter-finals with victory over Rafael Nadal's Spain in their second Group B tie on Tuesday.

The 18 nations have been split into six groups of three at the Caja Magica, with the pool winners and two best runners-up to play in the last eight of the first edition of the revamped tournament.

The teams face off in two best-of-three-set singles matches and one doubles rubber in each tie.

Khachanov and Rublev completed the clean sweep for Russia with a 7-6 (7-3), 6-4 doubles win over Ivan Dodig and Nikola Mektic.

Fancied Italians upset

Italy, who won their only Davis Cup in 1976, were the favourites in Group F with Fognini and Berrettini both having enjoyed excellent seasons - the former winning the Monte Carlo Masters and the latter reaching the ATP Finals.

The 20-year-old Shapovalov saved three set points before snatching the first set in a tie-break, only for Berrettini to level the match in a second-set breaker.

A clash without a single break of serve was decided by another tie-break, with Shapovalov reeling off the last three points to win after two hours and 52 minutes on court.

Berrettini and Fognini boosted Italy's hopes of making the quarters with a hard-fought doubles success over Shapovalov and Pospisil, winning 6-2, 3-6, 6-3.

Canada take on the United States on Tuesday, with Italy facing the Americans the following day.

Belgium made a victorious start in Group D with back-to-back singles wins against Colombia.

The South Americans are playing at the top level of the tournament for the first time, having never played in the old World Group.

Steve Darcis saw off Santiago Giraldo 6-3, 6-2, before world No. 11 David Goffin had to battle back from a set down to avoid a shock against 194th-ranked Daniel Elahi Galan Riveros, winning 3-6, 6-3, 6-3.

But the world No. 1 doubles pairing of Juan Sebastian Cabal and Robert Farah grabbed a historic win for Colombia by battling past Sander Gille and Joran Vliegen 6-7 (5-7), 6-4, 7-6 (7-3).