The singer, 38, is known to have had problems with Aguilera many years ago, but has since insisted that they buried the hatchet.
And while Aguilera was performing a tribute to Whitney Houston, the camera cut to Pink – who then went viral for appearing to cringe at her.
However, she has spoken out on Twitter to deny that that was the case.
She wrote: “Christina f**king killed it tonight for one of our favorite singers ever.
“This about Whitney, and I am in awe of Christina’s talent. Show the clip where I’m in tears, you negative Nancy’s.”
Aguilera did not respond online to Pink, but did Like her tweet.
Pink herself took to the stage twice last night: once on her own, and once as part of a duet with Kelly Clarkson, in which the pair sang REM’s Everybody Hurts in tribute to the emergency services.
Other notable performances came from a brave Selena Gomez, just months after a kidney transplant – but viewers cried foul by accusing her of miming.
Demi Lovato gave a well-received rendition of Sorry Not Sorry, Diana Ross delivered an epic medley, and Nick Jonas gave a rendition of Find You.
Big winners included Bruno Mars who scooped silverware for Artist of the Year, Favourite Pop/Rock Album, Favourite Pop/Rock Male Artist, Favourite Soul/R&B Male Artist, Video of the Year, Favourite Song – Soul/R&B.
Niall Horan took New Artist of the Year, Linkin Park took Favourite Artist – Alternative Rock, Coldplay scooped Tour of the Year and Collaboration of the Year was taken by Luis Fonsi and Daddy Yankee with Justin Bieber’s Despacito.
Despacito also won Favourite Song – Pop/Rock, while Drake was crowned Favourite Artist – Rap/Hip-Hop.
Lady Gaga won Favourite Female Artist – Pop/Rock, and Moana won Top Soundtrack.