FORMER champion Jason Day recovered from an early deficit to beat Ryder Cup hero Graeme McDowell in their group match in the WGC-Dell Match Play on Wednesday.
But the world number two then headed straight into the clubhouse for treatment after appearing to injure his lower back while hitting his tee shot on the 16th hole at Austin Country Club. McDowell, who holed the winning putt at Celtic Manor in 2010, holed from five feet for birdie on the third and was conceded the fourth after Day found trouble off the tee, but the Australian hit back by driving the green on the par-four fifth to set up a winning birdie.
Further birdies on the eighth and ninth took the US PGA champion into the lead and he doubled his advantage on the 11th when McDowell, who won the Volvo World Match Play in 2013, found water off the tee.
Day also birdied the 12th to move three up and pars thereafter were enough to seal victory, but the 28-year-old looked in considerable discomfort following his tee shot on the 16th and had to climb gingerly into a fairway bunker to hit his second shot.
In the same group, Thailand's Thongchai Jaidee had beaten England's Paul Casey 2&1, while there were also narrow victories for Charl Schwartzel over Danny Lee and Brandt Snedeker against Charley Hoffman.
World number one and Texas native Jordan Spieth was three up after six holes against 2014 Ryder Cup hero Jamie Donaldson, while Phil Mickelson had raced into a five-hole lead at the turn against Matt Fitzpatrick.
Players and caddies were wearing black ribbons in tribute to the victims of the terrorist attacks in Brussels, with Belgium's Thomas Pieters enjoying an early lead on former world number one Adam Scott in their group six contest. Fitzpatrick was unable to win a single hole against Mickelson and eventually lost 5&4, the biggest margin of defeat on the opening day so far.
Spieth remained in command with a three-hole lead against Donaldson after 11 holes, while McIlroy had lost the second hole to a birdie and the fourth to a par against Thorbjorn Olesen before bouncing back with a birdie on the fifth to halve his deficit.
Former Ryder Cup team-mates Sergio Garcia and Lee Westwood endured a rollercoaster contest which saw just three holes halved before Garcia emerged victorious on the 18th. Garcia was two up after three before losing the next four holes in succession, only to then win four holes in a row himself from the ninth to gain some semblance of control.
"It was very, very funny," Garcia said.
"We halved just three holes in the whole 18. Lee said to me on 17, 'We are gelling well!' It would have been better in a fourball. It was very up and down. I started very well and he hit a couple of poor shots, then he got on a great run and the last three or four holes he was making birdie or I was. I'm very happy with the putt I made on 18 to get the win."
