MADRID — Costume-wearing fans, boisterous crowds, exciting matches.

Old traditions were preserved when the revamped Davis Cup began a new era on Monday in Madrid.

As the 18-team Davis Cup Finals got underway in its new weeklong World Cup-style format at the “Magic Box” tennis complex, fans were encouraged to provide atmosphere, and delivered.

The Croatian marching band roused the center court.

Drum-beating Canadian fans lit up Stadium 2.

Dressed-up Belgians kept the crowd going in Stadium 3.

Umpires were made to work hard at all the courts by constantly asking for the fans to stay quiet before points.

“The atmosphere has been amazing,” said Canadian fun Pier-Anne Lussier. “It’s been really fun.”

On court, two-time champion Russia, Belgium, and Canada took an early lead in round-robin play.

Russia defeated defending champion Croatia after Andrey Rublev beat Borna Gojo 6-3, 6-3 and Karen Khachanov edged Borna Coric 6-7 (4), 6-4, 6-4.

“When you play not only for yourself but your country, you need to give extra toughness and extra fight,” Khachanov said. “It was a tough match. First time playing here in Madrid on hard court, opening match, extra pressure, it was important to start well.”

Belgium got the best of Colombia thanks to Steve Darcis’ 6-3, 6-2 win over Santiago Giraldo and David Goffin’s 3-6, 6-3, 6-3 victory over Daniel Elahi Galan.

“For me it’s big, I know it’s going to be my last time playing for Belgium, so I’ll try to do my best like always. It’s going to be a great week,” said the 35-year-old Darcis, who is planning to retire next year.

Canada edged Italy after Vasek Pospisil topped Fabio Fognini 7-6 (5), 7-5 and Denis Shapovalov outlasted Matteo Berrettini 7-6 (5), 6-7 (3), 7-6 (5) after nearly three hours.

The teams are playing only two singles and a doubles in each tie, with the group winners advancing to the knockout stage.