Nick Kyrgios beat Verdasco in Montreal

Nick Kyrgios began his US Open hardcourt run with a 6-3 4-6 6-4 victory over Fernando Verdasco on Tuesday under the watchful eye of new mentor Lleyton Hewitt at the ATP Montreal Masters.

Kyrgios, the world No. 41, is working alongside Australia's double grand slam winner in an informal capacity, with the 34-year-old elder statesman of the current Aussie game happy to help out the 20-year-old youngster.

But Kyrgios said the arrangement remains flexible and fluid, with Hewitt also attending to his own business on court as he goes into the final months of a career due to end early in 2016 after playing in his last Australian Open.

"He's not my coach. Let's clear that up now," said Kyrgios after his victory in 95 minutes over Spain's Verdasco in a first-time meeting featuring 15 aces off the Aussie racquet.

"He's more of a mentor. Lleyton is very kind to take time away from his family and his career to help me and Thanassi (Kokkinakis). We don't know how long it will last but it is a great help."

Kyrgios has not played since losing his only singles rubber in Davis Cup play last month after finishing a turbulent Wimbledon fortnight which was marred by outbursts and controversy from his side.

But the Australian may have regained some calm after a few weeks at home in Canberra.

"I came from a place where it's really cold right now," he said of the Australian capital, where readings this week dropped below freezing at night. "I've been practising indoors.

"Conditions here are tough, and the humidity doesn't help," he said on a day when play was delayed for two hours by rain. "I've never sweated so much as I did today."

Kyrgios called his win over Verdasco acceptable: "I was pleased to get a win over a quality opponent," he said before moving into a second-round clash with French Open champion Stan Wawrinka. "I'm really happy with myself. The courts here are bouncy and lively. I knew I had to take control even if I didn't serve that well.

"I'm pleased with how I finished in the third set. I competed well and that's the main thing.

"Stan is playing unbelievable tennis. He's got a big everything - forehand, backhand. I'll go out there, play my game and see how it goes."

In other first-round matches, 13th seed David Goffin started with an easy 6-2 6-2 defeat of American Steve Johnson while 14th seed Grigor Dimitrov beat Ukrainian Alexandr Dolgopolov 6-4 7-5 under leaden skies.

Top seed Novak Djokovic and number two Andy Murray were due to open later on a day still under threat from rain.