The season starts again on Friday.
Since their last meeting from June 7-9, the Red Sox have gone 32-16, a record topped by only the Yankees' (35-15) in the American League. With 52 games remaining, they are deadlocked atop the AL East.
As the teams meet for the first time in almost three months, it's back to square one. That underscores the significance of Boston's 8-1 record in the first nine meetings with New York.
For all the optimism surrounding the Red Sox, without that seven-game head-to-head cushion, the outlook would be far different right now.
Boston's early dominance against the Yankees has extended to the rest of the division. Against AL East opponents, the Red Sox are 28-12. Against everyone else? Just 40-40.
So what lies ahead for the Red Sox?
Their historic start against the Yankees recalls a cautionary tale.
For just the third time, the Red Sox have won at least eight of their first nine games against the Yankees in a season. That had occurred only in 1912 (9-0) and 2009 (8-1), according to the Elias Sports Bureau.
Entering the series, Boston has won seven straight against New York. That's tied for the third-longest streak for the Red Sox in the history of the rivalry.
Here again, 1912 and 2009 provide the most relevant historical comparisons. With half of their season series remaining, they also offer stark contrasts for how the rest of the series might unfold.
In 1912, the Red Sox won their first 14 games against the Yankees, and that still stands as their longest one-season streak against them. It included consecutive road sweeps of three and five games. Ninety-nine years later, the Red Sox have swept consecutive road series of three or more games for the first time since then.
Although the 1912 win streak ended at 14 games, Boston never took its foot off the gas pedal. By season's end, the Sox were 19-2 against the last-place Yankees (then known as the Highlanders). In the first season of Fenway Park, the Red Sox won a franchise-record 105 games and their second World Series.
Then there's 2009.
Again, the Red Sox started 8-0 against the Yankees, the second-longest single-season streak in the rivalry (a mark that could be tied Friday). In fact, along with the 1912 Red Sox and the 1990 Athletics (12-0), they were one of only three teams to start at least 8-0 against New York, according to Elias. Both of their predecessors went on to the World Series.
This start had a very different ending.
In the teams' final 10 meetings that season, Boston went 1-9. According to Elias, it was the first time in MLB history that a team won its first eight games against an opponent but failed to win the season series.
This weekend's series comes nearly two years to the day that the 2009 downward spiral began. A four-game sweep beginning on Aug. 6 reversed the gains from the first eight meetings. Not only did Boston slip to 6½ games out, but the nature of the losses sapped the momentum from the season.
Two years later, it provides a pause to the current optimism in Boston.
The series opener marked the end of the line in Boston for John Smoltz, who was designated for assignment after allowing eight earned runs in a 13-6 loss. He and Billy Traber each allowed nine hits, the first time two Red Sox pitchers did that in the same game since 1934.
That was followed by a 2-0, 15-inning loss in which Alex Rodriguez became just the fifth player in MLB history with a walk-off home run that broke a scoreless tie in the 15th or later. Still derided as "not clutch" and without a World Series to his name, soon neither statement would apply to A-Rod.
The Red Sox were again shut out in the third game. By Sunday, they had gone 31 straight scoreless innings, their longest stretch since 1974.
Four losses later, the season had a different outlook. The lesson? You can't discount the impact of momentum.
So how can the Red Sox avoid a repeat of 2009? It helps that the next six games against New York will be at Fenway Park.
A closer look at the first nine meetings of the season reveals just what had to happen for the Red Sox to go 8-1.
Dustin Pedroia is 15-for-30 against the Yankees this season. That came before he'd even found his stroke. Consider that in their most recent meeting, Pedroia was hitting .500 against the Yankees and .209 against everyone else. Since last facing New York, Pedroia is hitting .385 with a 1.105 OPS. What's in store against the Yankees now?
Meanwhile, CC Sabathia, who starts Saturday, probably would be in the driver's seat for the Cy Young were it not for what happened against the Red Sox. He's 0-3 with a 6.16 ERA against Boston and 16-2 with a 2.11 ERA against everyone else.
Contrast that with Josh Beckett. In 2010, he had a 10.04 ERA in five starts against the Yankees. This season, he's 3-0 with an 0.86 ERA going into his start on "Sunday Night Baseball."
Can those trends continue?
The nine remaining head-to-head games will go a long way toward determining the division title.
In each of the previous three seasons, the Red Sox and Yankees split the series 9-9.
With an 8-1 head start, that seems poised to change. Unless history repeats.
Jeremy Lundblad is a senior researcher with ESPN Stats & Information. He provides statistical analysis for ESPNBoston.com.