Gros Islet (St Lucia), July 10 : West Indies registered an 18-run win in the opening match of the five-match T20I series against Australia at the Darren Sammy National Cricket Stadium here. The hosts took advantage of a sensational batting collapse by Australia, who lost their last six wickets for just 19 runs on Friday. After being sent in to bat, West Indies scored 145/6 in their 20 overs. Andre Russell's first fifty in T20Is led West Indies to the below-par total. Russell's knock of 51 off 28 balls, with five fours and three towering sixes, lifted West Indies out of trouble after they had been reduced to 66/4 in 12 overs. Apart from Russell, Lendl Simmons (27) and Shimron Hetmyer (20) were notable contributors in a batting order which missed regular captain Kieron Pollard due to a hamstring injury. For Australia, Josh Hazlewood took three wickets for just 12 runs while Mitch Marsh took two wickets for 26 runs. Chasing a modest target of 145, the visitors posted 70 in the power-play for the loss of skipper Aaron Finch. By the 11th over, Australia were 108 for four with Marsh and Ben McDermott at the crease. Leg-spinner Hayden Walsh Jr, brought back for the over, took McDermott down with a googly and then took a return catch when Marsh drove straight to him in the next over. With 29 runs away from the target, Australia's free-fall continued. Walsh Jr took another wicket while left-arm pacer Obed McCoy clinched the last three wickets to put an end to Australia's misery at 127 with four overs remaining. The second T20I between the two teams will be played on Sunday. Brief scores: West Indies 145/6 in 20 overs (Andre Russell 51, Lendl Simmons 27; Josh Hazlewood 3-12, Mitchell Marsh 2-26) beat Australia 127 in 16 overs (Mitchell Marsh 51; Matthew Wade 33; Obed McCoy 4-26, Hayden Walsh Jr. 3-23) by 18 runs. /IANS