For the previous nine seasons, there were three certainties when the Boston Red Sox and New York Yankees did battle: The games would be sold out, or darn close to it. The games would be long — VERY long. And those sitting in the stands for games that often lasted more than three-and-a-half hours were watching a pair of World Series contenders: The Red Sox and Yankees both made the playoffs five times in a seven-year span from 2003 through 2009.

But the demise of the Red Sox over the last 12 months — they are 58-61 this season and 75-87 in their last 162 games, the equivalent of a full season — has removed most of the luster from the Red Sox-Yankees rivalry. The Sox, who are 12 ½ games behind the Yankees in the AL East and six games behind Baltimore and Tampa Bay in the wild card race, are all but assured of missing the playoffs for the third straight year and extending their streak of seasons without a postseason victory to four years.

Yet when the Sox and Yankees clash again tonight, August 17, in the opener of a three-game series, they will almost certainly take well over three hours to complete nine (or more) innings and they’ll do so in front of a capacity crowd at 50,291-seat Yankee Stadium.

Every single Red Sox-Yankees game since 2003 at Fenway Park has been sold out — the Red Sox’ current sellout streak began May 15, 2003, four days before the Sox hosted the Yankees for the first time that season. And the two teams haven’t played to a crowd below 46,000 since the new Yankee Stadium opened in 2009 and didn’t play to a crowd of less than 45,000 in their final 55 games at the old Yankee Stadium.

Buy Sell and Go with confidence at StubHub

So why do the two teams still play to full houses? Because people have long memories, and the baseball remains compelling.

“Hopefully I understand it, because I’ve been through it,” ESPN broadcaster and former Red Sox manager Terry Francona told TicketNews last weekend at Citi Field, where he was working the Mets-Braves game. Francona managed the Red Sox from 2004 through 2011.

“It’s great baseball. It’s great baseball on both sides. I always felt that way. Obviously, I rooted for one side more, which I don’t do now. But there are good players on both sides of the field.”

The Red Sox won the last two games between the teams by scoring the tie-breaking run in the ninth inning at Yankee Stadium on Saturday, July 28 and Sunday, July 29. The Red Sox won the July 28 game after the Yankees came back from a five-run deficit to tie it in the eighth inning on a two-run homer by Mark Teixeira off Vicente Padilla, with whom he’d exchanged harsh words earlier in the season

The Red Sox’ win July 29 evened the record between the two teams since 2003 at 87-87. The Sox and Yankees are also dead even when counting the 14 epic American League Championship Series games they played in 2003 and 2004. The Yankees eliminated the Red Sox on Aaron Boone’s 11th-inning home run in Game Seven in 2003 while the Red Sox came back from a three games to none deficit to win the 2004 ALCS on their way to winning the World Series for the first time in 86 years.

The tautness of the Red Sox-Yankees games lends a gripping feel to even the longest of the games between the teams. Of those 174 regular season contests since 2003, only 20 have been played under three hours, including only five of 63 since 2009. A remarkable 35 regular season games since 2003 have gone at least 3:30 while 17 have gone at least four hours.

The Red Sox and Yankees are in the record books for both the longest 18-inning doubleheader in history (eight hours and 40 minutes on August 18, 2006) and the longest nine-inning game ever (four hours and 45 minutes in the nightcap of that doubleheader). But time is not an issue for fans — or managers — when the games are good and the possibility exists that another classic game could be unfolding right in front of them.

“I don’t think I’ve ever really thought about it [in terms of time],” Francona said. “If it’s a good game, I don’t think the time matters. Bad games are when you look at your watch, whether you’re in the dugout or in the press box. A well-played game, you don’t look at your watch.”