The Finland international went down holding her face after a shove from Ella Toone, who had retaliated to a challenge from the Summanen late in the second half.
Toone was given a straight red card by referee Amy Fearn, which would have incurred a three-match suspension, but replays showed that the Man United attacker made contact with Summanen's shoulder rather than her face.
As a result, Toone's three-game ban was overturned, and Summanen was subsequently charged with successful deception of a match official, which she has now been found guilty of despite her denial.
Summanen will therefore miss Tottenham's upcoming FA Cup clash against Reading on Sunday and a trip to Manchester City in the WSL on March 5.
A statement from the FA read: "Tottenham Hotspur Women's Eveliina Summanen has been suspended for two matches following their WSL match on Sunday February 12 against Manchester United Women.
"The midfielder denied a charge for 'successful deception of a match official', which allegedly took place during the 80th minute and led to an opponent being sent off, and amounts to improper conduct.
"An independent Regulatory Commission upheld the charge during a subsequent hearing and imposed her two-match ban. Its written reasons will be published in due course."
Leah Galton and a Molly Bartrip own goal either side of Bethany England's strike gave Man United a 2-1 win over Tottenham in North London, leaving Marc Skinner's side top of the WSL table and Spurs - who have lost their last seven top-flight matches - down in ninth.