April 26th marked the worst home attendance in Arizona Diamondbacks history. The announced crowd of 12,215 filled only 25.2 percent of Chase Field, surely raising a red flag for the organization.

Enter the Diamondbacks’ “Ballpark Summer Pass,” a deal that proved hotter than Phoenix in July.

After announcing they would sell summer passes for the months of June and July for $50, the Diamondbacks sold their 4,000-ticket allotment in three-and-a-half days.

Since the deal started, average attendance has increased by more than 4,300.

“It was unbelievable,” Diamondbacks president and CEO Derrick Hall said. “It really brought a lift and a bunch of energy here to the ballpark.”

The Diamondbacks have 25 home games during those two months, translating to a cost of just $2 a game.

“We had been looking for a way to try out a more-or-less membership-type of option,” Hall said.

Before June, the Diamondbacks’ average attendance at Chase Field was 23,177. In the six home games since, that number increased to 27,479. When the club played the Milwaukee Brewers on Saturday, 40,195 were in the stands.

“That’s what people are looking for. They are looking for flexibility,” Diamondbacks fan Robert Strong, 57, said. “And options as far as prices and all that. I think this a good move.”

Fans access tickets for the game by using MLB’s Ballpark app, which let’s them know where they will sit two hours before first pitch. The summer pass also allow consumers the option to upgrade their seats for an additional fee.

The team’s success this season has surely helped. It was 26-19 when the deal was announced on May 21 and now sports the best home record in baseball (26-9).

“If they offered the same deal at this point last year would I have done it? Probably not,” Strong said. “Because they were just a hard team to watch last year.”

Entering Thursday’s game against Philadelphia, the Diamondbacks are 15 games above .500.

“The Phoenix market is unique and it’s technically a small market,” said Viet Do, 41, who purchased a summer pass. “I think you have to be a little innovated to get people in the seats when there is so much to do in the Phoenix market.”

Other clubs around the league are also offering their fans ticket deals.

The Oakland Athletics’ average attendance for games in 2014 was 25,045 in the Coliseum. This season it’s 17,028. The club is offering $19.99 monthly passes for home games from June to September.

Another team that saw a drop in attendance was the Padres, falling from 30,367 in 2015 to 25,073 this season. The club is offering $99 tickets for the first five home wins in the month of June.

The deals appeal to fans who don’t want to commit to season tickets.

The Diamondbacks’ offer, and their success on the field, has proved to be a winning formula.