Shane Lowry has shocked World number one Rory McIlroy to win their first round clash at the WGC Match Play in Arizona.

As it happened: Irish in action at WGC Match Play

After missing the halfway cut in Abu Dhabi last month - McIlroy's first tournament after switching to Nike clubs in a multi-million dollar deal - the Northern Irishman lost his opening match the man  ranked 68th in the world.

A team-mate of McIlroy back in their amateur days, Lowry marked his debut in the event with a last-green victory he will long remember for the way he followed chip-ins at the 11th and 12th with a conceded eagle on the next to go two up.

Golf's hottest young property won the 14th and 16th, but in between hacked left-handed into a bunker from the edge of a cactus bush and then sent his third shot flying over the green into more trouble.

There was just enough light for them to finish and although Lowry found two bunkers on the last McIlroy followed him into the greenside sand and after he had almost holed Lowry got up and down to win.

It is the third time in four years at the event that the top seed has gone out straightaway. Luke Donald lost last year to Ernie Els and in 2010 Steve Stricker was beaten by Ross McGowan.

McIlroy said: "I drove really well, but couldn't take advantage of that. If I'd hit my irons better it could have been a different story.

"I could have been three or four up early, but let him get back in the match and he had a nice little run.

"I just left myself a little bit too much to do."

As he spoke second seed Tiger Woods was beaten as well, going down 2&1 to fellow American Charles Howell.

A three-time winner of the title, it was also the third time Woods has gone out in the first round. Peter O'Malley and Thomas Bjorn have previously beaten him at the same stage.

At least he has a win under his belt already this year. The pressure is building on McIlroy as he heads into his defence of the Honda Classic next week.

Lowry stated: "To make par on the last was great and to beat him was even better.

"My knees were knocking over that final putt. I managed a couple of chip-ins which were huge - I had a bit of luck that I needed and I said to my caddie that he's not going to be liking this at all."

There was a danger of the top three seeds all going out when 2011 winner Donald came to the last all square with German Marcel Siem, but he birdied it.

Lee Westwood did go out, though, losing on the first extra hole to Spaniard Rafael Cabrera Bello, while in the other all-Irish clash Graeme McDowell defeated Padraig Harrington one-up.

There were wins too for Ian Poulter and Justin Rose, but all three Scots in the field went out.

Dubai Desert Classic winner Stephen Gallacher lost 2&1 to 2010 winner Ian Poulter, Paul Lawrie found American Scott Piercy too hot to handle and lost 4&3, then Richie Ramsay could not hold onto a two-hole after 11 playing fourth seed Louis Oosthuizen. The South African won on the 17th.

Jamie Donaldson, the only Welsh representative, was going home too. He lost 3&2 to Thorbjorn Olesen, the Dane he pushed into second place in Abu Dhabi last month.

English duo Chris Wood and David Lynn were hoping to pull off upsets against Masters champion Bubba Watson and US Open champion Webb Simpson, but it was not to be. The Americans won 2&1 and 5&4 respectively.

It will be Rose against Ryder Cup team-mate Nicolas Colsaerts next following contrasting victories.

The first world championship of the year is playing catch-up after an amazing snowstorm cut short the opening day and then another overnight meant no resumption was possible until 1pm.

Belgian Colsaerts easily dispatched American Bill Haas 5&4, but Rose breathed a huge sigh of relief when he saw off South Korean KJ Choi following the loss of a four-hole lead.

Fifth seed Rose was even in danger of falling behind at the 15th, but sank a 15-foot birdie putt and Choi missed from 12.

He did not even need to putt two holes later as his 42-year-old opponent got in trouble and conceded, but Rose said: "I said at the beginning of the week it comes down to that one moment in the round where you need to make something happen.

"That moment for me was on 15. I was looking like I was going one down. To make a putt when I really needed it feels good and I felt like that's what I've begun to do a lot recently.

"It'll be a tough game against Nicolas, but obviously one that I'm looking forward to - and I'll have to make some birdies."