At this time of year, it does not matter how a team wins, just that it wins.
A walkoff wild pitch helped Albuquerque (73-66) reclaim second place ahead of Round Rock (72-67).
"Not many, I can't even think of any off the top of my head," Castellanos said of seeing a walkoff wild pitch before. "That just happened. We could have won with a hit, a single, a sac-fly.
"We still battle. We're a good team, it just so happens we didn't make the playoffs. We're still a good team, we just got in a little slump there."
Castellanos smashed a 1-1 pitch off the fence just to the right of the center field hill for a one-out triple. He had to hold at third base when Matt Angle grounded out softly to shortstop.
The Express opted to intentionally walk Brian Barden to bring up Drew Butera, who was 0-for-4.
On a 1-2 count, Ryan Feierabend (6-5) threw a pitch in the dirt that catcher Eli Whiteside could not corral. The ball bounced to the left of home plate and Castellanos scampered home as Feierabend failed to catch Whiteside's desperation throw home.
"The big thing was Casty had a good read on it," manager Lorenzo Bundy said. "It didn't go that far away. It put more pressure on the catcher to make a good throw and it put more pressure on the pitcher who was running and then has to stop, catch the ball and make a tag at the same time."
The Isotopes trailed until the ninth inning when Castellanos ripped a one-out single up the middle and then stole second base.
After Angle struck out, Barden was down to his final strike when he lashed a single to right-center, scoring Castellanos. Butera then struck out to send the game to extra innings.
Round Rock had gone ahead early on Brendan Harris' two-out, solo home run in the second inning. That would be all the scoring in the game until the ninth as the pitchers on both sides dominated.
Former Isotope Josh Lindblom tossed five shutout innings for the Express, allowing just two hits and one walk while striking out four batters.
Lindblom was followed by rehabbing Rangers reliever Neftali Feliz, who gave up two one-out singles in the sixth inning and then proceeded to retire eight in a row.
"We had a couple opportunities with a guy on third and didn't get it done (against Lindblom and Feliz)," Bundy said.
Red Patterson was solid for Albuquerque, allowing just the home run in seven innings of work. He scattered four other hits, walked one and struck out seven.
"Red did a great job, Red was really good," Bundy said.
Onelki Garcia tossed a scoreless eighth inning, Peter Moylan zipped through the ninth and 10th and Kelvin de la Cruz (3-1) escaped a two-on, two-out jam in the 11th by striking out Chris McGuinness.
"No doubt about it the secret was the pitching today," Bundy said. "Eleven innings of one-run baseball, that's pretty good."
The Isotopes and Express will wrap up Albuquerque's 2013 home schedule Thursday at 6:35 p.m.