MARANA, Ariz. -- At the 2009 Dubai World Championship, Rory McIlroy and Lee Westwood were paired together in the first round. The season-ending event gave them both an opportunity to take the European Order of Merit. McIlroy was then a 20-year-old kid from Holywood, Northern Ireland, but he was already one of the more cocksure players in Europe. He knew Westwood well because they were both at the time represented by Chubby Chandler, the head of International Sports Management. They had a friendly rivalry.
Westwood shot a 66 in that first round at Dubai, 2 better than McIlroy. But what came next would come to define the fussy nature of their relationship.
"I didn't think I would find it as difficult as I did, to be honest," McIlroy said after that first round. "Lee's been around a lot longer than me. You want to try to concentrate on the tournament, but at the same time you're seeing what he's doing.
"It will be nice not to play with him, just to concentrate fully on my own score and on my own game."
Westwood, who went on to win the tournament and the Order of Merit that year, thought McIlroy's comments were immature, but useful motivation for him for the rest of the event.
"It was obviously a massive feather in my cap," Westwood said.
"There's nothing worse to say than that if you're Rory and there's nothing better for me than a competitor to say they are glad they are not playing with me.
"I read it in the press. I wouldn't have said it, but I've been on Tour 16 years and he's been on Tour three. Sometimes what you say off the golf course and the mind games you play are as important as the pressure you can put on people on the course."
Westwood wasn't surprised when McIlroy shot an 80 to throw away a 6-shot lead at last year's Masters. "I've played with Rory and he does snap-hook under pressure," said the 38-year-old Englishman.
When McIlroy took a very commanding lead after 54 holes at the U.S. Open in June, Westwood tried to bring some perspective. "They don't give trophies away on Fridays and Saturdays," he said glibly.
Twitter has been a natural outlet for their squabbles. McIlroy dates the Danish tennis star Caroline Wozniacki. In a tweet, Westwood called McIlroy "half Danish." McIlroy tweeted back, "At least I'm not English."
Last October, when the now-22-year-old McIlroy left Chandler's ISM stable, Westwood called it a "bizarre decision" on the social network. McIlroy responded by un-following Westwood.
Whatever strife remains between the two Ryder Cup teammates will supply a juicy subtext as they meet on Sunday morning in the semifinals of the WGC-Accenture Match Play at the Ritz-Carlton Golf Club at Dove Mountain.
McIlroy beat Sang-Moon Bae 3 and 2 in his quarterfinal match. Westwood got by Martin Laird 4 and 2. Mark Wilson will face Hunter Mahan in the other semifinal match on Sunday. The winners of the semifinal matches will meet in the 18-hole final in the afternoon. The losers will have a consolation match for third place.
It's a shame that Westwood and McIlroy will face each other in the semifinals and not the final, where either the No. 2- or No. 3-ranked player in the world can earn the No. 1 ranking with a win. The only solace is that one of these two men will get a chance in the final to supplant Luke Donald at the top.
What can we expect on Sunday from these fiery combatants? Will they be able to put aside their Twitter wars and bantering and have a quality match? Their mutual friend, Graeme McDowell, has called their skirmishes "jokes with jabs," but it's unlikely that you will see a whole lot of talking between them on Sunday.
"I think it's the match that most people wanted and definitely the match that I wanted," McIlroy said. "We definitely don't spend as much time together as we used to, but it's totally fine. He's obviously a rival of mine on the golf course. He's a guy that you look out every week in a tournament and he's the guy you feel like you have to beat to win.
"There's no ill feeling between me and him or Chubby or anyone. It's all been very, very positive."
But Westwood was less cheerful on the issue. "[Rory] doesn't want to spend time with the people that manage me, and I don't want to spend time with the people that manage Rory," he said. "But there's nothing strained about the relationship between the two of us."
Before their matches on Saturday, McIlroy and Westwood exchanged pleasantries. "I'll see you on the first tee tomorrow morning," McIlroy told him.
Both men will be playing in their first semifinal at the Match Play. Westwood has twice been No. 1 in the world in parts of 2010 and 2011, but McIlroy has never been so close to obtaining one of his dreams.
"I've been at No. 1 a couple of times. It would be a different way of thinking to me compared to Rory who hasn't been No. 1," Westwood said. "He may be thinking about it, but my main goal is to play well or play as well as I've been playing [Sunday] morning and try and win that match."
Still, both players will undoubtedly feel the pressure. Westwood wants to put his younger rival in his place and McIlroy wants nothing more than to beat the man who has consistently thrown barbs at him since he turned pro in 2007.
"The thing that would worry me is getting too much up for [Sunday] morning knowing that if you do win you have to go through and play [Sunday] afternoon, so you have to try and conserve your energy the best you can," McIlroy said.
Westwood disagrees. "I can never quite figure that mentally drained one out," he said. "Why would you get mentally drained when you get into positions that you work for and practice hard for? You should be in those positions enjoying yourself."
Come late Sunday morning, we'll know which player had the mental fortitude and the game to win one of the biggest matches in the tournament's history.
Farrell Evans covers golf for ESPN and can be contacted at email@example.com.