Gambling revenue at Plainridge Park Casino tumbled by more than 5 percent in August, as managers of the state’s first casino continued to sacrifice short-term profits in hopes of building a loyal clientele.

The Plainville slots parlor attracted plenty of business last month, notching its fourth-highest monthly total in bets — $178 million — since opening in June 2015.

At the same time, the casino sharply increased player winnings, sending more gamblers home happy but cutting into its profits.

Plainridge retained less than 7.5 percent of wagers, the lowest in the casino’s short history and more than 2 percentage points lower than its first full month of operation in July 2015, according to figures released Thursday by the Massachusetts Gaming Commission.

By offering greater payouts, the casino is seeking to expand its customer base in a crowded gambling market, specialists said.

“Plainridge is trying to stay competitive and build itself up,’’ said Clyde Barrow, a University of Texas professor who closely follows the New England casino industry. “It’s a delicate judgment, deciding what percentage a casino should keep as its revenue.’’

Penn National, which owns Plainridge Park Casino, declined to comment.

Plainridge brought in $13.1 million in August, about $25,000 less per day than it did in July, Compared with last August, revenue fell by more than $2 million, or about 14 percent.

Barrow said Plainridge managers have decided to take a smaller bite of wagers, known in the industry as “coin-in,’’ by setting slot machines to deliver more wins per spin. That pushes more money back to gamblers.

Experienced players realize the odds are against them, he said, but are looking for slot machines that provide enough wins to extend their gambling time.

“Players want longer periods to play with the same amount of money,’’ Barrow said. “That’s the enjoyment and excitement of gambling.’’

The casino has clearly shifted its strategy. In its first eight months, Plainridge withheld about 8.75 percent of all bets. In the past six months, that amount, known as the hold, dropped to 7.5 percent.

Plainridge took in $160 million in its first year, falling far short of forecasts.

Small changes to the hold have a major impact on a casino’s bottom line. If Plainridge had kept 8.75 percent of revenue in August, for example, it would have generated an additional $2.5 million in revenue.

Plainridge’s hold percentage in August was lower than either of the Connecticut casinos, Foxwoods Casino Resorts and Mohegan Sun. In Rhode Island, the hold is calculated in a way that makes comparison difficult. But in recent months, all three casinos have steadily pushed down their hold percentages.

Plainridge enjoys a monopoly on slot machine gambling in Massachusetts, but may soon face increased competition.

The owners of Twin River Casino in Rhode Island are gearing up for a statewide ballot question to authorize a new casino in Tiverton, R.I., just a couple hundred feet from the Massachusetts state line in Fall River and about a 45-minute drive from Plainridge.

That vote is scheduled for November.

Construction is underway on a $2.1 billion Wynn Resorts casino in Everett and a $950 million MGM Resorts casino in Springfield.

Sean P. Murphy can be reached at smurphy@globe.com. Follow him on Twitter @spmurphyboston.