Nick Kyrgios has fought back to keep alive Australia’s Davis Cup hopes, seeing off a determined Steve Darcis in a five-set thriller in Brussels.

Kyrgios won 6-3 4-6 6-7 (7-5) 6-1 6-2 against the wily world No.70 who had looked set to inflict more misery on Australia – seven years after relegating the 28-time champions from the World Group.

The crucial victory levelled the tie at 1-1 ahead of Saturday’s doubles rubber after David Goffin earlier beat a spirited John Millman.

Kyrgios stormed imperiously through the opening set, sending down eight aces without losing a point in five service games.

The controversial tennis player from Canberra stirred up the home fans by cupping his ear to them after taking the lead, a move that only seemed to inspire Darcis, who was playing in his 21st tie for his country.

Darcis finally found a way to return the Kyrgios serve and broke in the second game of the second set and held on to level the match.

A titanic third set was decided in a tie-breaker after Darcis fought tooth and nail to save six break points in the fourth game, and a set point when 5-6 down before eventually taking the set.

However, the world No.20 silenced the crowd in emphatic fashion by taking the fourth set 6-1 as Darcis struggled to counter his huge serve, with Kyrgios saving a break point with 227kph ace.

Kyrgios continued to serve well in the decider, but Darcis managed to stay in the contest, saving multiple break points before succumbing on serve in the fourth game.

It allowed Kyrgios to see out the match to seal one of his best victories in an Australian shirt.

Goffin prevailed 6-7 (7-4) 6-4 6-3 7-5 against Millman, who was making his Davis Cup debut.

The world No.12 was made to work hard for his victory by the 185th-ranked Queenslander, who was only called into the team by captain Lleyton Hewitt on Thursday.

—AAP