Former champions Milos Raonic and Grigor Dimitrov stormed into the second round of the season-opening Brisbane International tennis tournament with comprehensive wins on Monday.

Raonic, the 2016 champion, demolished Slovenia's Aljaz Bedene 6-0, 6-3 while Dimitrov, who won the following year, sailed past Japan's Yoshihito Nishioka 6-3, 6-4.

Both men have career-high world rankings of three, but Raonic and Dimitrov have each slipped over the past 12 months and sit at 18 and 19 respectively.

The big-serving Raonic fired down 18 aces in his win over Bedene and won 93 per cent of his first serves in a match that only last 47 minutes.

Dimitrov was also in complete control against 23-year-old Nishioka, the world number 76.

“I felt I was actually hitting the ball quite all right for our first match of the year,” he said.

“It was a good day overall. There were a few things that I would like to maybe improve on the next match, but overall I think it's off to a positive start.”

Dimitrov was troubled by an ankle injury towards the end of last season and barely played in the last few months of 2018.

But he said he used the time away from the court to re-evaluate his game.

“I just actually felt that in those months I've learned a lot about myself,” he said.

“I learned things that I need to do better, things that I could improve off the court.

“So overall I actually felt that they were very successful months off the court.”