Mills inserted Paredes for Chris Johnson after Johnson singled with two outs in the top of the inning. Paredes didn't advance, as the next batter lined out to second base.
"I put him in a situation that was kind of tough for him right there, but at the same time, he's a guy that will score from first base on a double," Mills said. "We wanted to win the game."
In the bottom of the inning, Lucas Harrell (0-1) walked Zimmerman and Michael Morse with one out. Wilton Lopez replaced Harrell, and got Jayson Werth to hit a bouncer to Paredes. The rookie made a nice play to spear the grounder, but then overthrew second baseman Jose Altuve and Zimmerman scored. Werth was credited with a single.
"When I saw him at second base, I said we have to try and make an out at second," Paredes said. "Bad throw. That happens."
Houston has dropped six of seven and is four losses from its first 100-loss season. The Astros are one of three teams — Colorado and the Los Angeles Angels are the others — never to lose 100, according to STATS, LLC.
Instead of sounding frustrated after the tough loss, Mills said his young players would be able to chalk it up as a learning experience. The Astros have 15 rookies.
"You try to simulate game situations all the time," Mills said. "You can simulate as much as you can, but it's tough to simulate bottom of the 11th and the winning run at second base. They are growing pains, but at the same time you need to go through it. We can talk him through it and go from there."
The extra-inning loss wiped out a strong performance by starter Bud Norris, who allowed three runs — two earned — on five hits in seven innings. Norris has won just once in his last 11 starts.
Norris fell behind early after Zimmerman hit a two-run homer with one out in the bottom of the first.
"The first inning I definitely wasn't in my groove yet," Norris said. "Zimmerman made me pay."
The Astros scored off Tom Milone in the top of the third on Clint Barmes' double, an infield out and a sacrifice fly by Norris.
Houston tied the game when Johnson's sacrifice fly scored Altuve in the fourth.
The Astros took a 3-2 lead in the sixth on Carlos Lee's leadoff double and a two-out RBI single by Barmes. Milone left after the single. He pitched 5 2-3 innings, allowing three runs and eight hits.
Norris didn't allow another run until the seventh. Danny Espinosa walked with one out, and took third on a wild pickoff throw by Norris. Espinosa then tied the game at 3-all Chris Marrero's single.
"It got away a little bit, hit him right on the back," Norris said. "Not much you can do there. But it changed the scenario, and unfortunately the run scored."
Tyler Clippard (3-0), Washington's fifth pitcher, worked two scoreless innings for the win. The Nationals had lost 12 of 15.
NOTES: Houston LHP Sergio Escalona sprained his left ankle when he tripped on a glove in left field during batting practice. "I felt a little pop inside. Thank God, it just was a sprained ankle," Escalona said. He will be re-evaluated in Houston on Monday, but the ankle was swollen after the game and Escalona said he didn't think he'd pitch again this season. ... The Astros claimed RHP Lance Pendleton on waivers from the New York Yankees. Pendleton will join the club on Saturday and be used out of the bullpen, Mills said. ... LHP Wandy Rodriguez (10-10) will start for Houston on Saturday against LHP John Lannan (9-11). Rodriguez is 4-1 with a 4.98 ERA in eight starts against the Nationals.