Andy Murray made a winning start to 2019 but said he does not know how much longer he will be able to play top-level tennis after hip surgery.
Britain's former world number one beat Australian wildcard James Duckworth 6-3 6-4 at the Brisbane International in his first match since September.
Scot Murray, 31, struggled to contain his emotions as he told how last year had been "really hard".
Also in the first round, Briton Johanna Konta beat Sloane Stevens 6-4 6-3.
Murray is a three-time Grand Slam winner but currently ranked 240 in the world after only playing six tournaments in 2018.
"It's not easy to sort of sum up in one sentence or one answer," he said at the event, one of the warm-up competitions for the Australian Open, which starts on 14 January.
"It's been a really hard 18 months, a lot of ups and downs - it's been tricky to just get back on the court competing again.
"So I'm happy I'm back out here again. I want to try and enjoy it as much as I can and just try and enjoy playing tennis as long as I can. I don't know how much longer it's going to last but we'll see."
Murray broke wildcard Duckworth three times in a match that lasted just short of 90 minutes.
The double Wimbledon champion will next face number four seed Daniil Medvedev, ranked 16 in the world,
Murray earlier said farewell to 2018 with a tongue-in-cheek Instagram post where he pretended to be drowning his sorrows.
"Celebrating the end of 2018. What a s*** year that was," he wrote.
Konta 'trying to create something new'
In her first meeting with 2017 US Open winner and world number six Stephens, Konta survived two break points in the opening game before winning in one hour 52 minutes.
"The first three games took about half an hour, so there was very little in it, especially in that first set at the beginning," Konta said.
"I'm just very happy I was able to maintain my level quite consistently throughout."
British number one Konta, 27, will play Australia's world number 46 Ajla Tomljanovic in the second round.
"The most important thing is to keep moving forward," she said.
"I'm not trying to recreate something that I had. I'm trying to create something new and something better. I just keep looking ahead and I keep trusting in the work that I do.
"Nothing ever is straight sailing and a constant upward trajectory. I'm enjoying what I do - even through the challenges."