As a result, the Nationals scored some early runs and hung on for a 4-2 win over the D-backs in front of 19,549 at Nationals Park.
"All he really had was his four-seamer, and they were pounding it," D-backs manager Kirk Gibson said.
Alberto Gonzalez and Ian Desmond led off the first with singles, and one out later, Ryan Zimmerman brought them both home with a single to left.
"I didn't have the feel of any pitches in the first couple of innings," Saunders said. "It seemed like I fell behind hitters, put hitters in hitter's counts. When you do that to some good hitters, and they've got some good hitters over there, they made me pay for it."
Zimmerman, who moved up to second when left fielder Gerardo Parra threw home to try and get Desmond, scored one out later on a single by Michael Morse.
The Nationals added to their lead one inning later when Wil Nieves led off the frame with a home run to left-center.
It was quite a contrast from 10 days ago when Saunders allowed just one run on five hits to go the distance against the Nationals in Phoenix.
"They were a lot more aggressive," Saunders said. "I think they knew I was going to be around the strike zone. It was just a matter of locating early on, and I just didn't do that."
The Nationals clearly had learned from that game.
"He definitely throws a lot of fastballs," Zimmerman said. "If you let him get ahead of you, he's obviously more effective, just like any pitcher, but we wanted to hit the fastball, because his secondary pitches are more effective. If we can get to the fastball, we don't have to worry about the curveball or changeup. That was kind of the plan. We had a chance to do more damage, but he's got good stuff."
Zimmerman and his teammates didn't have to worry about the secondary pitches, because Saunders didn't have them in the first two innings. After that, though, he made a mechanical adjustment courtesy of pitching coach Mel Stottlemyre Jr., and that seemed to do the trick.
From the start of the third inning until he left with a pair of runners on in the seventh, Saunders allowed just three hits.
"I just tried to minimize the damage and keep us in the ballgame as best I could," said Saunders, who fell to 1-2 since coming to the D-backs from the Angels.
With the way John Lannan was pitching, though, the four runs proved to be too much of an obstacle to overcome.
The left-hander continued his mastery against the D-backs. Lannan has allowed just three earned runs in 26 career innings against Arizona, a far cry from the 5.44 ERA he had posted this year against the rest of baseball.
Arizona finally broke through in the fifth when Mark Reynolds drew a one-out walk and Stephen Drew followed with a triple to right.
Parra then drove in Drew with a single to center to pull the D-backs to within two.
"Normally he leaves a lot of hittable balls over the plate, and today he was hitting the corners pretty good and kept us off-balance with his changeup and his cutter," Reynolds said. "Besides the one inning, we weren't able to string things together."
Reynolds was then asked if he meant that Lannan leaves hittable balls over the plate to other teams, because the D-backs have never seemed to hit him.
"He has a five ERA for a reason, I guess," Reynolds said. "Today he had one of those games where he was just hitting the corners and not really leaving much to hit."