Brazilian Monteiro beat world number 63 Dolgopolov of Ukraine 6-3, 6-3 in the first-round of the event held in North Carolina in the United States.

Not long before the match, a huge amount of money was placed on Monteiro.

It meant he started the contest as favourite, despite being ranked 51 places below Dolgopolov in the world rankings.

The TIU announced it would be investigating the match shortly after it had ended.

A number of bookmakers also suspended betting before it had begun. 

There is no indication either player has done anything wrong.

"The TIU was made aware of concerns over betting patterns during the match," a statement from the anti-corruption body reads. 

"As with all match alerts, the TIU will assess, make a judgement and take appropriate action on the information received through its co-operative agreements with betting operators."

Former top-20 player Dolgopolov, who lost his first meeting with Monteiro on clay at last month’s Swiss Open in Gstaad, failed to muster a break-point opportunity on his opponent’s serve as he fell to defeat in 55 minutes.

"I can confirm we suspended the match [betting] due to the suspicious moves in prices pre-match," a spokesperson for betting firm Ladbrokes told BBC Sport.

"This was flagged to relevant authorities right away."

The TIU is an initiative of the Grand Slam Board, the International Tennis Federation (ITF), the Association of Tennis Professionals and the Women’s Tennis Association, who are said to be jointly committed to a zero tolerance approach to corruption in tennis.

Tennis has faced significant match-fixing problems, particularly at levels where prize money is low.

It was the sport involved in 59 per cent of suspicious betting alerts recorded by the European Sport Security Association (ESSA) during the second quarter of this year.

The ESSA, the international betting integrity body, said it had reported a total of 53 cases across five sports - tennis, basketball, football, handball and volleyball - to the relevant authorities for further investigation.

Thirty-one of these came in tennis, with football representing the next highest with 15 cases.

In March, ITF President David Haggerty announced plans for tours with a limit of 750 male and 750 female players.

It is thought that around 14,000 are currently competing among the full-time ranks, with nearly half of these failing to win any prize money, which is thought by many to be a reason why some are tempted by corruption.