Lannan limited the Padres (38-61) to one run over eight innings. Gaudin left after seven innings, he, too, having allowed just one run. Both pitchers received no-decisions and both probably deserved better.
Two innings before Washington's Austin Kearns won the game with an RBI single, a defensive miscue by the Padres allowed an unearned run to score and give the Nationals (30-68) a 2-1 lead.
San Diego second baseman Luis Rodriguez dropped the relay on what in all likelihood would have been a double-play ball on a grounder hit to shortstop Everth Cabrera. The results were not good, as Adam Dunn bounced a single to center field that gave the Nationals what turned out to be a short-lived lead.
"That play has got to be made," Padres manager Bud Black said. "That was a ball that should have been turned."
Washington closer Mike MacDougal got the first two outs of the ninth inning before he left a fastball out over the plate for rookie right fielder Kyle Blanks, who sent it deep into the left-field bleachers to tie the game at 2.
"It takes the wind out of your sails a little bit. He got all of it -- it was a no-doubter," Nationals manager Jim Riggleman said.
It was the third home runs for Blanks, all coming in his past six games.
"That's what I was looking for," Blanks said of the 97-mph fastball from MacDougal. "I got it and didn't miss it. He throws hard. But it helps when you're looking for that one."
The Padres didn't like what they saw from Lannan, as he got ahead quickly and got the Padres to go after pitches early in the count, getting nearly as many flyouts (10) as groundouts (11).
Lannan retired 11 consecutive hitters at one point and needed just 81 pitches to work through eight innings. On a humid afternoon and with the game-time temperature as 86 degrees, the Padres didn't make him sweat much.
The Padres finally made him work a little in the sixth inning when Will Venable drove a pitch off the base of the wall in left-center field for a one-out double. One batter later, Kevin Kouzmanoff doubled into the gap in right-center to plate Venable for a 1-0 San Diego lead.
In the fifth inning, Lannan got three outs on four pitches.
"He's a guy who is so efficient that he looks better to hit than he is," Venable said. "It's not riding [the ball] that hard, it's just funky enough. You get in trouble not giving him as much credit as he deserves."
While Lannan was clearly more efficient on Sunday, he wasn't any more successful than Gaudin, who walked two over the first six innings and allowed three hits, two, ironically enough, to Lannan.
It was not until the seventh inning when the Nationals finally touched Gaudin for a run, as Josh Willingham clubbed a home run into the left-field bleachers -- on a 1-2 pitch no less -- to tie the game.
It marked the first time Gaudin had yielded a home run since June 23 against the Mariners. All told, Gaudin had gone five starts and 37 innings without allowing a homer.
"I just wanted to get quick outs ... it was hot," Gaudin said.
Gaudin was done after seven innings, yielding one run on five hits. He had five strikeouts and two walks. It marked the 10th quality start of the season. Not bad for a player the Padres signed to a Minor League contract in April.
"I thought that he held his stuff through the game on a hot, muggy day. That was a game that was going to come down to a pitch or two," Black said. "A game like that, you can't let things slip."
Also on Sunday, Padres All-Star first baseman Adrian Gonzalez set the club record for most consecutive games played (306) when he appeared in the game on defense in the seventh inning. Gonzalez broke the record he tied Saturday, one that was set by Steve Garvey.
Gonzalez also has the longest active streak of consecutive games played among all Major League players.