According to social media statistics service Famecount.com, Gaga recorded 5,635,460 followers early on Thursday, less than 10,000 behind Spears.
The experts expect Gaga to top Spears by Friday.
Spears became to top celebrity on Twitter.com earlier this summer when she passed Ashton Kutcher.
The experts predict Justin Bieber will have toppled Lady Gaga by the end of the year as he builds on his 4.5 million Twitter followers.
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