Spain beat Serbia in their opening tie of the Davis Cup group stage on Wednesday as U.S. Open champion Carlos Alcaraz watched from the sidelines.

Alcaraz, who made his Davis Cup debut in a qualifying tie against Romania in March, only arrived in Valencia on Tuesday after becoming the youngest men's world number one in history with last weekend's triumph at the U.S. Open in New York.

With Rafael Nadal also absent against a Serbia team missing Novak Djokovic, Albert Ramos-Vinolas won the opening rubber against Laslo Djere 2-6, 7-6 (7/5), 7-5.

Roberto Bautista Agut secured the tie for Spain by defeating Miomir Kecmanovic 7-6 (7/5), 7-6 (7/5) in the second singles.

Marcel Granollers and Pedro Martinez will play Nikola Cacic and Dusan Lajovic in the doubles.

Lorenzo Musetti and Matteo Berrettini gave Italy the perfect start to their campaign with victory over Croatia in Bologna.

The 20-year-old Musetti saw off Borna Gojo 6-4, 6-2 in the first rubber of the best-of-three Group A tie.

Former Wimbledon runner-up Berrettini had to fight back from a set down against Cincinnati Masters champion Borna Coric, but won 6-7 (4/7), 6-2, 6-1.

Simone Bolelli and Fabio Fognini edged a final-set tie-break against Nikola Mektic and Mate Pavic to complete a 3-0 sweep.

Italy have high hopes of claiming only a second Davis Cup title and first since 1976. Their top-ranked player Jannik Sinner could yet be ready to play against Argentina on Friday.

Cameron Norrie rallied from a set down to overcome Taylor Fritz 2-6, 7-6 (7/2), 7-5 and to bring Britain level at 1-1 against the U.S. in Glasgow.

Tommy Paul took down Dan Evans in three sets in the opening rubber.

Germany won their first Group C tie against France after Tim Puetz and Kevin Krawietz defeated Nicolas Mahut and Arthur Rinderknech in the doubles in Hamburg.

Jan-Lennard Struff beat Benjamin Bonzi 6-4, 2-6, 7-5 to give the home team the lead, before Adrian Mannarino levelled with a 6-4, 6-3 win over Oscar Otte.