McIlroy used the New Year's Eve fireworks at Sydney Harbour as the spectacular backdrop for his midnight proposal, with the sporting love match hitting Twitter to make their big announcement.

"Happy New Year everyone! I have a feeling it's going to be a great year!! My first victory of 2014 #shesaidyes!!" McIlroy tweeted yesterday morning.

Wozniacki, 23, proudly posted a photo of her diamond engagement ring, saying she said "YES!!!" after McIlroy popped the question.

"Happy New Year everyone! Rory and I started 2014 with a bang! . . . I said YES!!!" Wozniacki tweeted.

Wozniacki and McIlroy began dating in 2011.

The two former world No 1s celebrated New Year's Eve in Sydney as Wozniacki prepares for the Australian Open starting on January 13.

The Dane withdrew from this week's Brisbane International citing a sore right shoulder but still plans to contest the Sydney International starting on Sunday.

McIlroy's engagement rounds out a memorable month for the Northern Irishman after he ran down Adam Scott for a spectacular victory in the Australian Open at Royal Sydney for his first tournament success of an otherwise disappointing 2013 on the course.

After starting the season as world No 1, McIlroy ended the year ranked sixth - but is celebrating his greatest conquest in Australia.

McIlroy and Wozniacki both posted photos of the Sydney Harbour Bridge and fireworks, as well as a picture of a giant rock on her left hand when revealing their engagement.

They won't be the first famous golf-tennis double act to get married.

Greg Norman - like McIlroy a two-time major champion - wed fellow former world No 1 Chris Evert in 2008.

Norman and Evert's marriage lasted only 15 months before they divorced. AAP