Andy Murray reached the Australian Open quarter-finals for a third year running after Mikhail Kukushkin retired through injury while trailing 6-1 6-1 1-0.
The effects of two five-set matches in rounds two and three took their toll on Kukushkin, who pulled out with a left hip flexor problem after 49 minutes.
"It was hot on the court and it is good for me that I have conserved energy," said British number one Murray.
Next up for the fourth seed is Jo-Wilfried Tsonga or Kei Nishikori.
Murray has winning record against both men and he approaches that match on Wednesday feeling fresh.
"I played him [Kukushkin] a few weeks ago at Brisbane and it was three tough sets and I expected another tough one today," said Murray.
"I hadn't seen him play before Brisbane and he hit some huge shots early and had me work."
"It was hot on the court and it is good for me that I have conserved energy.
"It is tough for him for that to happen in the fourth round of a Grand Slam for the first time."
Kukushkin beat Gael Monfils in five gruelling sets on Saturday and those exertions seemed to hinder him in the scorching Melbourne heat.
Three unforced errors in the first game handed Murray a break and although the Scot struck again for a 3-0 lead.
Kukushkin finally displayed some fight to hit back in game four, only to relinquish his serve again after pushing two backhands wide.
The world number 92 gave an indication he was not 100% fit when he called for the trainer at the next change of ends, and Murray broke once more to wrap up the 22-minute first set.
As in his third-round victory over Michael Llodra, Murray was playing close to the baseline and attacking Kukushkin serve and groundstrokes with real aggression.
A lapse in focus saw the world number four relinquish an early break in the second set with a poor backhand into the net.
But a struggling Kukushkin, who started rushing the net in a bid to shorten points, handed the momentum straight back.
Murray breached his defences with some clean hitting for 5-1 up before serving out another 22-minute set to love.
Having required more treatment and then lost his serve for an eighth successive time, Kukushkin called it quits.
