BOSTON -- The frustration that had Bobby Valentine breathing fire from the top step of the Red Sox dugout, and resulted in his second ejection as Red Sox manager, wasn't brought on by a single pitch.

It wasn't brought on by the strike called against Dustin Pedroia in the bottom of the ninth, or the ball called against Alfredo Aceves a pitch before he surrendered the winning run in the top of that same frame. It wasn't even brought on by a bad day for the umpires. It was brought on by a weekend's worth of what he believed to be injustices.

“An accumulation,” Valentine said. “Like when Alfredo struck the guy out, on a pitch that the whole ball is on the plate, he calls it a ball and (Roger Bernadina) gets an RBI. I've got guys busting their butt, battling their butt off. It's not right.

“Good umpires had a real bad series this series. Real bad series.”

What that ignores, of course, is that for his team the series was even worse.

When Bernadina's double delivered Bryce Harper from first, then Pedroia stranded the potential equalizer by striking out, the Nationals secured a 4-3 win and a sweep of three-game sweep of the Red Sox, who lost five of six on a homestand that ended Sunday — and hit the road with bigger problems than the men in blue.

They're now 29-31 on the season after losing six of seven overall. They're last in the American League East later than they've been in 15 years. Their closer lost both of the tied games he's entered over the past week. Their supposed staff ace couldn't protect a seventh-inning lead in either of his two starts on the homestand. And their hitters struck out a total of 30 times in the three games against Washington.

They're playing at a level where a franchise that had never won a game at Fenway Park comes in on a weekend and wins three in a row, where a young team that had failed in 12 of its previous 13 chances to complete a sweep can do it this time by being better with the game in the balance, and where a member of the Nationals can make the following claim to reporters afterward.

And do so with little the Red Sox can rebuke.

“They have a good team,” Tyler Clippard said, “but I think we're better. We're a lot better.”

The Nationals are certainly good, as baseball's second-best record makes obvious. They have the best earned run average in the majors, and a good-enough lineup. But what's concerning for the Sox is the widening gap that seems to divide them and the rest of their division.

The East divisions of the American and National leagues went head to head this weekend — and the AL squads won three of the four other series, combining to go 9-3 outside of Boston. So by the time the Red Sox boarded their flight to Miami, where the Marlins await, the East was home to the three best winning percentages in the AL. And the Sox themselves needed to play better than any of them have played to this point, a .588 clip, just to win the 89 games they did a season ago.

“Aggravates the (heck) out of me,” starter Jon Lester said of being in last place. “I hate going out there and losing.”

Some of Sunday was circumstantial. Lester gave up the lead on a wall-scraping double that would've been a flyout in every other big-league ballpark. Then there was the umpiring of Alan Porter, who probably cost Aceves a strikeout that would've ended the winning inning, and made Pedroia's last-ditch at-bat more difficult by giving Clippard a pitch off the corner.

“You don't want them to come into play,” Pedroia said. “It's hard enough playing the game against good pitching and good players, so it's pretty disappointing.”

“I felt there were some pitches that could've definitely went our way, but that's the way the game is,” said catcher Jarrod Saltalamacchia.

But ultimately he understood it wasn't where the game – the series, the homestand – was lost. “You can't really rely on the umpires. We've got to do it ourselves, and that's what it boils down to.”

And what Valentine should really be boiling about.

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WITH Sunday's loss, the Red Sox fell to 14-19 at home this season – but they still insist that'll turn around.

“There's 162 games,” Pedroia said. “We might win 50 in a row here, and you guys will write articles about how great we are at home. I don't know.”

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THE original plan was tossed aside when Jacoby Ellsbury suffered a shoulder subluxation in the home opener. And Mike Aviles' .281 on-base percentage in that role wasn't getting it done. But when Scott Podsednik batted leadoff on Sunday, it marked the 12th time in 13 games that the top spot in the Boston lineup was held by a hitter who wasn't good enough to play in the major leagues in 2011.

In those dozen games with Podsednik or Daniel Nava batting first, the Sox have faced Justin Verlander, Stephen Strasburg, Gio Gonzalez and played six games without Pedroia, yet — perhaps indicating the true importance of a leadoff man, they still averaged 4.62 runs in those tilts. Entering Sunday, the major-league average was 4.29.

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The Red Sox announced Sunday's game as their 745th consecutive regular-season sellout, the most ever for an American major-league sports franchise. The Portland Trail Blazers sold out 744 straight regular-season tilts in a streak that ended in 1995.

Dave D'Onofrio covers the Red Sox for the New Hampshire Union Leader and Sunday News. His e-mail address is ddonof13@gmail.com.