Castro hasn't hit in the top spot yet in 2013, batting second in 30 of his 34 games. He also hit third once and fifth three times, but Castro has been the lead-off hitter in 74 career games, carrying a .319 average with eight homers and 31 RBIs.
Dave Sappelt, sent down earlier this week, had led off against lefties before this while David DeJesus does it against righties. Manager Dale Sveum said moving Castro to the top spot wasn't a hard decision.
"Just kind of a process of elimination really," Sveum said. "[The] two choices were really him or [Cody] Ransom and having Ransom in the lineup; hopefully he's going to hit a home run, [and] I'd like him to do it with somebody on base. It's just kind of the way the lineup's going to be now when a left-hander pitches."
Sveum said he could still shake the batting order up against a lefty if Julio Borbon is in the game in center. But the job belongs to Castro most of the time versus southpaws.
Since he's hit in bunch of spots, Castro said the switch to batting first is fine with him.
"It [doesn't] matter where he puts me," Castro said. "Everywhere he tries to put me, I try to do my job. I like it. I like [batting first]."
Also, Edwin Jackson will again try for win No. 1 Saturday when he starts the middle game of this series. Jackson (0-5) gets a bit of a homecoming here as he pitched with the Nationals last year, but said before Friday's game that returning to Washington doesn't give him any extra motivation.
"I have seven ex-teams, eight ex-teams probably," he said. "It's a pretty familiar situation for me. I have a lot of homecomings."
Here's tonight's lineup:
1. Starlin Castro, SS
2. Cody Ransom, 3B
3. Anthony Rizzo 1B
4. Alfonso Soriano LF
5. Scott Hairston, RF
6. Wellington Castillo, C
7. Ryan Sweeney, CF
8. Darwin Barney 2B
9. Jeff Samardzija, P