Having said that, the Yankees didn’t look like defending World Series champions last night in a 9-7 loss to the Red Sox.

Predictably, CC Sabathia struggled early, as he often does, and the Red Sox took advantage. Last season the big lefty got off to a 1-3 start with a 4.85 ERA in his first six starts. Last night he squandered a 5-1 lead, allowing five runs and six hits in 5 1/3 innings even though he outpitched Josh Beckett (five runs, eight hits in 4 2/3 innings) by a hair. This wasn’t a surprise after a bad spring training in which Sabathia had an ERA in the mid-6s.

“I actually felt great. I thought my stuff was good,’’ said Sabathia. “Early in the game I was strike one right there, then I’m trying to throw down and away and I’m missing down. I started to nibble just a little too much and got into hitter’s counts, and this is a tough lineup to pitch to when you’re behind on the count. I normally don’t do that, especially with a lead. It was one of those nights where I lost my focus.’’

Predictably the Yankees mashed. Jorge Posada and Curtis Granderson hit back-to-back homers in the second inning against Beckett, Posada had three hits, Derek Jeter had two.

One surprise: the run prevention, pitching-based Red Sox also hit. Not a surprise was that the Yankee bullpen couldn’t get to Mariano Rivera. An assortment the likes of Chan Ho Park, Damaso Marte, and Joba Chamberlain makes one think the Yankees’ bullpen may not be quite as good as Boston’s.

“They still have a very good lineup,’’ said Sabathia. “They have professional hitters that if you make mistakes they’re going to take advantage. They work the count. They’re still a very good lineup.’’

What a mixed night for Posada.

He started things off for the Yankees with a solo homer in the second, the fourth Opening Day homer of his career (only Babe Ruth has more for the Yanks, with five) en route to a 5-1 lead. Posada knocked in New York’s seventh run with a clutch single in the seventh to give the Yankees a 7-5 lead and his single in the ninth after two outs made Jonathan Papelbon squirm for just a moment before he retired Granderson for the final out.

The dark side occurred in the bottom of the seventh in a 7-7 tie when Marte, the last man to arrive to the Yankees’ clubhouse yesterday, threw a high inside fastball to David Ortiz that Posada didn’t read well. In fact, he missed it, with Kevin Youkilis rumbling in from third (after Marte had thrown a wild pitch to put him there following a double) with the go-ahead and what proved to be the winning run.

Posada said there wasn’t a cross-up but rather “a mixed location.’’ He said he called for a fastball down in the zone and it came up and got past him.

Sabathia said he and Posada were on the same page. “I was just missing,’’ he said. “Instead of coming right at them with a four-run lead I started nibbling on the corners instead of just putting the ball in play.’’

“They made adjustments,’’ Posada said. “[Sabathia’s] changeup hurt us. He threw some good ones down. Once or twice around the lineup the changeups started getting up a bit. His fastball was still at the same velocity late in the game.’’

Posada said the way the Yankees started out against Beckett, “I thought we had a good game plan against him.’’

As Posada said, the game turned when Dustin Pedroia poked a two-run homer into the Monster seats in the seventh.

“With Chan Ho, I thought one pitch really changed the whole ballgame,’’ the catcher said. “The pitch to Pedroia was supposed to be a little further inside. And the pitch [by Marte] to Youkilis [for the double off the Wall], he wasn’t deep in there enough. Damaso just got a little wild.’’

Posada, 38, has been one of the best-hitting catchers in baseball for a long time. He’s been a big part of the Yankee world championships and will go down as one of the great Yankees. In the past couple of years there have been questions about his defense, fair or unfair. He went through the A.J. Burnett situation last season when Burnett felt uncomfortable throwing to Posada despite protests from both players that everything was fine. Jose Molina, who left the Yankees and signed with the Blue Jays, became Burnett’s personal catcher. But with Molina gone, Posada and Burnett have reunited; Posada will catch Burnett tomorrow.

Posada claimed before the game that he and Burnett “never had a problem. We just had one bad game.’’ That game was June 9 at Fenway and Burnett was gone after five innings and after shaking off Posada several times.

Yet Molina caught Burnett even in the postseason, including Games 2 and 5 of the World Series.

Posada made it sound as if the issue was more with manager Joe Girardi than anyone else. “I think Girardi is the perfect guy to answer that question,’’ said Posada. “I think he’s got the best point of view on that. Ask him.’’

“There have been a lot of guys that have had different catchers than the starting catcher during the season,’’ Girardi said. “Greg Maddux did it all the time. It was not a huge story in Atlanta. Randy Johnson always had one wherever he was. To me this took on a bigger picture because we’re in New York. It became a big story, but as far as having a problem, I wasn’t concerned about that. I didn’t necessarily see a huge problem.’’

One game does not a season make. Last year we learned that eight losses in a row against the Red Sox don’t necessarily wreck a season.

But the Yankee had last night’s game in their back pocket, at least twice.

“Judging by the way things went, this is going to be very interesting,’’ said Granderson about the rivalry. “We’re going to play one another a few times and we’re going to end the season against each other. This is going to be very interesting.’’