Novak Djokovic began the season with a gritty victory over former Wimbledon runner-up Kevin Anderson at the ATP Cup, as Rafael Nadal also launched his year with a win.
On duty for Serbia against South Africa in the team event, Djokovic both fed off and appeared to be distracted by a noisy Brisbane crowd as he battled to a 7-6 (7-5) 7-6 (8-6) victory.
At one stage, Djokovic railed at umpire Mohamed Lahyani when he was denied the chance to challenge a line call.
In the second-set tie-break, Anderson could not take a set point on his own serve. Rather than going to a decider, Djokovic snatched his chance to seize victory in straight sets to put Serbia in charge of the tie.
Anderson played only five tournaments last season because of knee and shoulder problems, so to push the world number two so hard was a highly creditable effort.
"What a way to start the year," Djokovic said in his on-court interview, after repeating his 2018 Wimbledon final victory over Anderson.
"I'm pretty pleased with my game. To be honest, considering the fact that he was playing at the very high level, I thought it was a fantastic match."
Djokovic's win put Serbia 2-0 ahead, after Dejan Lajovic had edged past Lloyd Harris in three sets, while Nikola Cacic and Viktor Troicki teamed up for a 52-minute stroll past the South African pair of Raven Klaasen and Ruan Roelofse, dropping just five games, to clinch a 3-0 team success.
The tournament is being contested by 24 teams, split between venues in Brisbane, Sydney and Perth, with many of the world's top players taking the chance to compete ahead of the Australian Open later this month.
World number one Nadal beat Nikoloz Basilashvili 6-3 7-5 in Perth as Spain overcame Georgia in Group B, with team-mate Roberto Bautista Agut drubbing world number 679 Aleksandre Metreveli 6-0 6-0. Pablo Carreno Busta and Feliciano Lopez earned a doubles win to make it a perfect day for the Spanish team.
Borna Coric enjoyed an impressive win, seeing off world number four Dominic Thiem 7-6 (7-4) 2-6 6-3 in Sydney as Croatia beat Austria 3-0.
Argentina fended off Poland 2-1 in Sydney and Japan were 3-0 victors over Uruguay in Perth.
Gael Monfils and Benoit Paire both scored singles wins as France earned a 2-1 success against Chile in Brisbane. That match was arguably more notable for the two beaten Chilean singles players - Cristian Garin and Nicolas Jarry - pairing up in doubles to register a 7-5 6-2 win over the acclaimed duo of Nicolas Mahut and Edouard Roger-Vasselin.