The alert came after Swiss 15th seed Timea Bacsinszky's 6-1 6-1 victory over Russia's Vitalia Diatchenko on Aug. 30.
It is the second allegation of match-fixing to surface at a grand slam this year. At the Australian Open, a global bookmaker suspended betting on a mixed doubles match after unusually large amounts were bet on it.
"We are aware of the alert and at this point it is a matter for the Tennis Integrity Unit," United States Tennis Association spokesperson Chris Widmaier told Reuters. "We certainly have full confidence in the TIU to follow up properly and quickly regarding this matter.
"That being said, all betting alerts need to be properly investigated.
"But in this situation we are fairly confident that nothing nefarious has happened here but the TIU will undergo its normal process to ensure that there is no suspicious activity here."
The TIU said in a statement the Bacsinszky and Diatchenko match is the only alert it has received from the year's final grand slam which wraps up on the weekend with the women's final on Saturday and men's on Sunday.
"As with all cases, the TIU will assess, make a judgment and take appropriate action on the alert information received and obtained for the first round singles match between Vitalia Diatchenko and Timea Bacsinszky," said the TIU.
Widmaier said the USTA had been made aware of suspicious betting patterns surrounding the match.
The TIU has memos of understanding with betting houses around the world. If an anomaly appears in betting patterns they inform the TIU who investigate.
The TIU cautioned that "an alert on its own is not evidence of match-fixing”.
"As with all cases, the TIU will assess, make a judgment and take appropriate action on the alert information received and obtained for the first round singles match between Vitalia Diatchenko and Timea Bacsinszky played at the U.S. Open on 30th August," the TIU said in a statement on Wednesday.
The TIU noted there can be other reasons for unusual betting including "incorrect odds-setting, well-informed betting, player fitness, fatigue and form as well as playing conditions and personal circumstances".
(Additional reporting by Toby Davis; editing by Ed Osmond / Ian Ransom)
