Croatia dethroned holders France to win the Davis Cup for the second time as Marin Cilic beat Lucas Pouille in straight sets to seal the victory.
Serena Williams re-established her customary superiority, hammering Daria Gavrilova 6-1, 6-2 to reach the second round of the Cincinnati Masters on Monday.
Alexander Zverev got his Rome title defence underway at the Italian Open on Wednesday with a straight-sets win over Italy's Matteo Berrettini as the German bids for back-to-back Masters triumphs after success in Madrid.
Japan's Yoshihito Nishioka said his comeback from knee surgery will "take time", after letting a one-set lead slip in a first-round loss to Benoit Paire at the Dubai Championships on Monday.
Adrian Mannarino sent defending champions France through to the Davis Cup quarter-finals on Sunday after sealing victory over the Netherlands, while Croatia knocked off Canada to follow Spain through.
Lucas Pouille throttled Belgium's Steve Darcis 6-3, 6-1, 6-0 in Sunday's decisive fifth rubber to clinch a 10th Davis Cup title for France in front of a passionate Lille crowd.
Rafael Nadal secured the year-end world number one ranking with a 7-5, 6-3 second-round victory over South Korean Hyeon Chung at the Paris Masters on Wednesday.
Temperamental Australian Nick Kyrgios was fined $10,000 and lost another $21,085 in prize money on Wednesday after storming off midway through his first-round match at the Shanghai Masters.
Australia's hopes of reaching a first Davis Cup final in 14 years were shattered on Sunday when Belgium fought back from an overnight deficit to win their semi-final 3-2 and set-up a title showdown with neighbours France.