BOSTON — First the Boston Red Sox lost their grip on the American League Championship Series. Then they lost their series lead to the Houston Astros. Now they must rally for two wins at Minute Maid Park for the pennant.

J.D. Martinez expects to have fun.

“We’re going to Houston and we’ve got Nate on the mound, and I’m excited about it,” Martinez said, referring to Nathan Eovaldi, who won his start in Houston last Saturday. “I think it’s going to be a fun game — a fun last two games.”

Fun? It was a simple but refreshing choice of words from Martinez, Boston’s designated hitter, considering the circumstances. Martinez had struck out in all four of his official at-bats in Games 4 and 5, part of a team-wide funk that has whipped the bat rack like an arctic blast on a hot summer day. After punishing pitchers for most of October, the Red Sox have hit .131 in the last two games, falling behind the Astros, three games to two, in the series.

On Tuesday, a parade of Houston relievers shut down the Red Sox to even the series. On Wednesday it was Framber Valdez making the best start of the baseball postseason, an eight-inning clinic on how to tame sluggers with sinkers.

Martinez reviewed his at-bats, he said, and found no pitches he could have handled well. It is easier, it seems, to flush a game you had no chance of winning.

“Nobody is that perfect,” Martinez said of Valdez. “It’s very hard to go out there and have those repeat performances.”

Valdez is by far the most imposing Astros starter, and on Wednesday night, Manager Dusty Baker said he had not yet decided who would pitch Game 6. Eighteen years ago, as manager of the Chicago Cubs, Baker went home with a 3-2 lead in the National League Championship Series, and Mark Prior and Kerry Wood lined up to face the Marlins. It did not end well.

“I was feeling confident at that time, but you’ve got to get the job done,” Baker said. “You can feel confident all you want to, but taking the last breath and the final life out of anything, it’s a tough road. They’re going to fight you until the end.”

He added: “I feel good. I don’t feel great.”

Baker’s current players also have reason to be wary. In 2019, the Astros lost Games 6 and 7 of the World Series at home to the Washington Nationals. The year before — after they had stopped using their system of illegal electronic sign-stealing that helped them win the World Series in 2017 — the Astros dropped the final three games of the A.L.C.S. to the Red Sox.

“We did it before,” Red Sox catcher Christian Vázquez said. “We won three games in Houston in 2018. We need to win two, so why not this year, too? They have a great team, but I like my team. I don’t doubt my team.”

Boston earned 92 victories this season, a strong total for most teams but rather ordinary for the Red Sox, who have won at least 93 games in half of their seasons since 2000. After holding first place in the A.L. East for most of the first four months, the Red Sox trailed every day after July 30 and won a wild-card berth on the final day of the regular season.

Now, after eliminating two division rivals, the Yankees and the Tampa Bay Rays, and unloading on the Astros in Games 2 and 3, the Red Sox are scrambling again.

“This is our story,” Martinez said, speaking with reporters in a conference room. “We’ve been written off all year; I don’t think anyone in here, either, thought we were going to be here. We know what we’re capable of, and I think no one is not believing in themselves or not believing in our team that we can go out there and go off.

“We split. We won two in a row, they won two in a row. So it’s very possible.”

Of course, the Red Sox were hoping for more as they took their positions for the eighth inning of Game 4. They had a 2-1 lead in the game and the series, and needed six outs to push the Astros to the brink of elimination. Then Jose Altuve blasted a first-pitch homer off Garrett Whitlock, and from that point on, the Astros have outscored the Red Sox by 17-1.

“We know we can hit; two games doesn’t mean that all of a sudden we’re not a good offensive team,” Red Sox Manager Alex Cora said, adding later, “I don’t see it as a slump. It’s two games. Obviously, it’s a series. But we’ve been really good offensively the whole month.”

Cora said he was not considering lineup changes for Game 6, even with some hitters struggling, like Hunter Renfroe, who is 1 for 14. The Red Sox have slammed 22 homers this postseason, a club record, and Minute Maid Park is a haven for the long ball.

Martinez would know; he hit his first career home run there as an Astro in 2011, and his first postseason grand slam there last weekend. Now Martinez and the Red Sox will play in Houston again with a chance to win twice and claim the pennant. What could be better?

“It’s a must-win, like the wild-card game,” Martinez said. “It’s a situation our team is familiar with. So, I don’t know — it should be fun.”