SEATTLE — Boston starter Daisuke Matsuzaka left last night’s start abruptly before the start of the bottom of the fifth inning, apparently hampered by a sore back.

Trailing 3-0, Matsuzaka came out to make his warmup tosses before the bottom of the fifth. But after the second, he could be seen grabbing his lower back.

Catcher Jason Varitek immediately summoned trainer Paul Lessard and manager Terry Francona from the visitors’ dugout and they all soon converged at the mound, joined by home plate umpire Eric Cooper.

After a few minutes, Matsuzaka left the mound with Lessard. David Aardsma took over for Matsuzaka.

The scene was reminiscent of the first week of March, when staff ace Josh Beckett, bothered by back spasms, came out of a start before throwing a pitch, having wrenched his back during warmup throws.

Beckett didn’t pitch for the Sox again until the first week of April, missing the team’s trip to Japan.

Matsuzaka, who came into last night undefeated, at 8-0, had allowed three runs on four hits through the first four innings. He had struck out two and walked none, throwing 65 pitches — 46 for strikes.

Lugo, Francona tossed

In a bizarre development in the bottom of the fifth, shortstop Julio Lugo and Francona were both ejected by third-base umpire Angel Hernandez.

Lugo apparently took exception with Herandez’s ruling that Seattle DH Raul Ibanez checked his swing on a pitch by Aardsma. From his position at short, Lugo said something to Hernandez, who responded by tossing him from the game.

An enraged Lugo then rushed toward Hernandez to protest his ejection. Hernandez mostly ignored him as Francona raced out to defend his player.

Soon, Francona was gesturing and jawing in an animated fashion with Hernandez, and he, too, was ejected.

Alex Cora took over at short for Lugo, while Brad Mills managed the rest of the game for the Sox.

The ejections were the fifth and sixth for Red Sox personnel this year and third on the current road trip. David Ortiz, Manny Ramirez and hitting coach Dave Magadan had been run, with Magadan’s ejection taking place last Friday in Oakland.

Sox lead in early balloting

One of the perks of winning a pennant is the opportunity to serve as the manager for your league’s All-Star team the following summer. So it is that Francona will, for the second time in the last four seasons, direct the American Leaguers on July 15.

He’s already begun the task of thinking of which players to select as extras, though changes in fan and player balloting has taken away some of those decisions.

Yesterday, he learned that five of his own players — catcher Varitek, first baseman Kevin Youkilis, second baseman Dustin Pedroia, DH Ortiz and left fielder Ramirez –– are leading at their respective positions. The first batch of results were released yesterday.

Francona won’t apologize for the prominence of his own players in balloting.

“Because of our success and our popularity,” he said, “we’re going to have a lot of guys get votes. It’s kind of a reward for the team’s success and their personal success. There’s no getting around it — our fans are everywhere. I don’t see the need to apologize for that.”

Nor will Francona apologize if it turns out he’s managing a lot of his own players in Yankee Stadium, the site of this summer’s game, though Yankee fans in attendance might find that unappealing.

“It will be an unbelievable All-Star Game to be at,” said Francona. “Think about it: the last one at Yankee Stadium (which closes after this season). I can’t imagine a lot of (New York) fans will be thrilled that I’m sitting in the dugout. But it will be exciting.”

In addition to the five Sox players leading in the voting, Matsuzaka and Jonathan Papelbon are almost certain participants.

Youkilis remains on shelf

Youkilis remained out of last night’s lineup against the Mariners for the second straight night, still hampered by some soreness in the top of his right hand. Once again, Sean Casey got the starting assignment at first.

Youkilis underwent precautionary x-rays late Monday, which proved negative, and still isn’t sure about the origin of the injury.

The Sox are hopeful that Youkilis can recover and be in the lineup today against Seattle lefty Erik Bedard. Then again, as Francona pointed out, lefties have actually hit Bedard better this year, batting .347 with just four stirkeouts in 49 at-bats, compared to right-handers, who are hitting .183 in 126 at-bats.

Cash cashes in at plate

Catcher Kevin Cash will get the start tonight with Tim Wakefield scheduled to start for the Sox.

Cash, who made the club over veteran catcher Doug Mirabelli in spring training, has been a surprise offensively, hitting .314, though, admittedly, he hasn’t had a great deal of playing time (51 at-bats).

Still, over his last five games, Cash is 6-for-19 and has reached base in 10 of his last 12 games with at least one at-bat.

That’s impressive for someone who came into this season with a career batting average of .167.

“He worked a lot over with winter with (hitting instructor Magadan),” said Francona. “I think having some success early (in the season) certainly helps, especially for bench players. But in spring training, his approach was good and it’s carried over.

“He doesn’t swing at a lot of balls and he’s gotten some big hits. We’ll see where he is at the end of the season, but he’s done a good job. He’s worked hard and it’s paid off.”

Extra bases

Red Sox lefty Jon Lester was named co-winner of the American League Player of the Week honor, sharing with Detroit’s Magglio Ordonez. Lester, of course, threw a no-hitter nine days ago against the Kansas City Royals. He joins Ramirez and Youkilis as previous winners of the award this season. … Ramirez jokingly invited teammates and media alike to a party in his hotel room Monday night to celebrate the occasion of his 2,000th career game, going so far as to shout out the room number for all to hear. According to the Elias Sports Bureau, among players who’ve reached that milestone, Ramirez is 10th in homers (498) and sixth in RBI (1,635). … Wakefield and pitching coach John Farrell spent some time on the field at midafternoon yesterday talking with Seattle pitcher R.A. Dickey, who also throws a knuckle ball.

smcadam@projo.com