World number three McIlroy had been the most determined European player all week at Hazeltine National, but an 18-hole singles battle against America's top player Patrick Reed took every ounce of energy he had.
"I am running on fumes," McIlroy told reporters following Europe's 17-11 loss to the US in the 41st Ryder Cup.
"I won three points. I wish I could have been better, but I did all I could.
"There is not much more I could have done."
Also Read
McIlroy lost to Reed 1-up in a epic showdown that lasted 18 holes and kicked off the singles matches on Sunday morning.
On Saturday, McIlroy had security eject a heckler that had made a crude comment to him as he walked towards a tee box.
"A couple of people out there crossed the line. We will take it on the chin," McIlroy said.
It is a partnership that McIlroy wants to take into the next Ryder Cup in two years in France and beyond.
Pieters continued his strong play on Sunday by beating another long hitter J.B. Holmes 3 and 2.
McIlroy said Pieters reminds him of another Belgian golfer, Nicolas Colsaerts, who had an impressive Ryder Cup debut in 2012 at Medinah the last time the event was held in the US.
- 'Better than Colsaerts' -
===========================
"He (Pieters) was like Nicolas Colsaerts a few years ago. No offence to Nicolas, but Pieters is a lot better," McIlroy said.
McIlroy was critical of the course setup at Hazeltine this week saying that it rewarded players for poor shots.
"It was more beneficial to them," he said. "It didn't seem like bad tee shots were being punished as much as they should have.
"Any advantage you get when you are the home team, you take it."
McIlroy said Europe are looking to build a team for the future and that is one of the reasons they decided to include six rookies this year.
He is looking forward to the 2018 Ryder Cup in France and threw out a few names of people he would like to see become the next team captain.
"Looking towards Paris, there is Lee Westwood, (Padraig) Harrington or Thomas Bjorn. Any one of those guys could do it," McIlroy said.
"Because of our team culture and they way we all get along, it could be any one of those guys.
Disclaimer: No Business Standard Journalist was involved in creation of this content