O’Connell senior Olivia Giaquinto finished the marathon with a blast.

On a second day of softball, after 18 innings over four hours to begin the Washington Catholic Athletic Conference championship game Tuesday and another hour-long rain delay pushing back the restart of a grueling bout with No. 3 St. Mary’s Ryken nearly 26 hours later, Giaquinto’s swing was worth waiting for.

With the bases loaded in the top of the 19th inning, the O’Connell first baseman blasted a belt-high outside pitch over the center field fence at Holy Cross Academy to account for as many runs as the two teams combined to score in Tuesday’s 18-inning first act.

Propelled by Giaquinto’s grand slam, a star-turn from sophomore pitcher Kathryn Sandercock and timely defensive play, O’Connell reclaimed the WCAC trophy with a 7-2 win Wednesday in Kensington.

“This could have been a one-inning day. This could have been another 18-inning day,” said Giaquinto, a Harvard commit. “I don’t think anyone ever felt tired at any point because it was just, the next inning, this is going to be the inning.”

The meeting of the Knights has become an annual May tradition. O’Connell and St. Mary’s Ryken have decided the last four WCAC championships. Thanks in part to Giaquinto’s second clutch home run in as many postseason games, the trophy is headed back to Arlington after back-to-back titles by the team from Leonardtown.

St. Mary’s Ryken had already come back in the bottom of the ninth and 11th innings to force a 2-2 tie Tuesday before umpires called the game for darkness.

Senior All-Met pitcher Madison Aughinbaugh, who was named WCAC player of the year for the second year in a row, threw about 270 pitches in the first 18 innings, racking up 24 strikeouts Tuesday. When she tried to warm up on Wednesday, the Fordham commit said she could barely will the ball across the plate.

Junior Katie Prebble relieved her to start the 19th inning, walking the first three O’Connell batters before facing Giaquinto, who led a comeback against Elizabeth Seton in a Monday semifinal at Holy Cross by blasting a first-pitch, game-tying solo home run in the bottom of the seventh.

The final would not have lasted more than nine innings without Prebble, whose two-out single scored Aughinbaugh and gave St. Mary’s Ryken (21-2, 17-2 WCAC) new life after Giaquinto crossed the plate on junior Kayla Turner’s single in the top of the ninth.

Prebble knew she would probably have to pitch as early as Tuesday night, but she said she felt unprepared. She walked six batters and allowed another home run to Turner, who picked an opportune time for her first high school homer.

“It was hard to stay calm when all that pressure was on me,” Prebble said. “Every single time we play them it’s so intense, and I think they feel it, too.”

The pressure on O’Connell (19-5, 14-3) was eased by Sandercock, a sophomore James Madison recruit. Sandercock pitched a complete game, striking out 17 and retiring the last 24 batters in a row.

“With these kids it’s been growing pains all year. It really has been,” O’Connell Coach Tommy Orndorff said. “[Sandercock] has been a thrower. I think the past two weeks, she’s become a pitcher.”