Southeastern Connecticut’s casinos reported Tuesday that their September slot-machine revenues were down by more than 5 percent over the same month last year, extending their string of declines to 15 straight months.

Mohegan Sun kept $44.6 million in slots winnings, 5.5 percent less than the $47.2 million it kept the previous September. Foxwoods Resort Casino kept $35.9 million last month, 5.6 percent less than the $38 million it kept a year ago.

The year-over-year declines largely have been attributed to competition from MGM Springfield and Encore Boston Harbor, Massachusetts casinos that opened in August 2018 and this past June, respectively.

Figures released Tuesday by the Massachusetts Gaming Commission afforded the first year-over-year comparison of MGM Springfield’s gaming revenues. They show the western Massachusetts casino kept $14.8 million in slots revenue last month, 18.4 percent less than the $18.2 million it kept the previous September, its first full month of operation.

MGM’s table-games revenue was down by 42 percent, falling from $8.8 million in September 2018 to $5.1 million last month.

In September, its third full month, Encore Boston Harbor kept $21.9 million in slots revenue and $27.1 million in table-games revenue. The table-games revenue was more than five times as much as MGM’s.

The Connecticut casinos do not disclose their table-games numbers on a monthly basis.

Mohegan Sun sent $11.2 million in September slots revenue to the state. Foxwoods paid $9.4 million.

b.hallenbeck@theday.com