McIlroy, the current world number three, overcame American Zach Johnson in the round of 16 by sealing a one-up victory.

The Northern Irishman then went on to face another golfer from the United States in Chris Kirk and produced a dominant performance on his way to a 4&3 success to set up a heavyweight clash with Day in the last four.

“I feel like I've improved each and every day,” said four-time major winner McIlroy.

“And getting wins, as well, you do get momentum with every single round that you get through.

“You can feel it build and you can go with it and that's what I've been able to do.”

Day, who came into the competition in Texas off the back of winning the Arnold Palmer Invitational on March 17, had been suffering from back spasms earlier on at the tournament but showed no signs of injury during a confident 3&2 win over Brandt Snedeker in the first knockout round.

Day proved too strong for Brooks Koepka in the quarter-finals as he booked a meeting with McIlroy by beating the American by the same scoreline.

The 28-year-old from Queensland, who won the tournament in 2014, will become the new world number one when the rankings are released on Monday after American Jordan Spieth’s miserable year continued when he lost 4&2 to South Africa’s Louis Oosthuizen in the last 16.

The defeat not only ended his pursuit of the WGC-Dell Match Play Championship crown but saw Spieth relinquish his status as the top ranked player in the world.

Oosthuizen, who has one major title to his name after claiming The Open title in 2010, then progressed to the semi-finals with a 2&1 triumph over American Dustin Johnson.

His opponent in the last four stage will be the surprise package of the tournament as he will face 52nd seed Rafa Cabrera Bello of Spain, who earned a semi-final berth by ousting America’s Ryan Moore 2&1.

The semi-finals and final will be held tomorrow.