Madrid - Canadian Vasek Pospisil claimed a surprise victory over Italy's Fabio Fognini to put his side in control of their Davis Cup Finals tie on Monday, while Andrey Rublev got Russia off to a winning start on the opening day.
World No 12 Fognini slumped to a 7-6 (7/5), 7-5 defeat by the 150th-ranked Pospisil at the Caja Magica.
Rising star Denis Shapovalov could send Canada to the top of the early Group F table with victory in their second singles rubber against world No 8 Matteo Berrettini.
In-form youngster Rublev eased to a 6-3, 6-3 victory over Borna Gojo, who is playing for reigning champions Croatia in the absence of the injured Marin Cilic.
Russia are without US Open runner-up Daniil Medvedev after he pulled out due to exhaustion following a gruelling end to the season.
Rafael Nadal's Spain are the other team in what promises to be a closely-contested Group B.
Belgium also took an early advantage as Steve Darcis saw off Colombian Santiago Giraldo 6-3, 6-2.
The South Americans are playing at the top level of Davis Cup tennis for the first time.
The nations have been split into six groups of three, with the pool winners and two best runners-up to play in the quarter-finals of the first edition of the revamped tournament.
The teams will face off in two best-of-three-set singles matches in each tie, with one doubles rubber.
Results from the Davis Cup Finals in Madrid on Monday:
Russia 1 Croatia 0
Andrey Rublev (RUS) bt Borna Gojo (CRO) 6-3, 6-3
Karen Khachanov (RUS) v Borna Coric (CRO)
Karen Khachanov and Andrey Rublev (RUS) v Ivan Dodig and Nikola Mektic (CRO)
Belgium 1 Colombia 0
Steve Darcis (BEL) bt Santiago Giraldo (COL) 6-3, 6-2
David Goffin (BEL) v Daniel Elahi Galan Riveros (COL)
Sander Gille and Joran Vliegen (BEL) v Juan Sebastian Cabal and Robert Farah (COL)
Canada 1 Italy 0
Vasek Pospisil (CAN) bt Fabio Fognini (ITA) 7-6 (7/5), 7-5
Matteo Berrettini (ITA) v Denis Shapovalov (CAN)
Simone Bolelli and Lorenzo Sonego (ITA) v Vasek Pospisil and Denis Shapovalov (CAN)