It's a safe bet the Boston Red Sox are aware of it, too, though they should be feeling good about getting their second look at the right-hander.
Following his second defeat, Tanaka will again try to become the first in the majors to reach 12 victories as the Yankees and Red Sox play the second game of their three-home series Saturday night.
Tanaka (11-2, 2.11 ERA) was 6-0 with a 2.17 ERA over eight starts before taking his first loss against Chicago on May 20 at Wrigley Field. Pitching through a steady rain, he allowed three earned runs and struck out seven in six innings of a 6-1 loss.
It was his second outing against the Cubs, who managed two hits against him in eight innings of New York's 3-0 home win April 16.
Tanaka bounced back from the Wrigley defeat by winning five straight starts with a 1.26 ERA and 40 strikeouts over 35 2-3 innings. However, it was another team getting its second glance at his repertoire that ended the dominant stretch.
Tanaka pitched well but didn't get a decision in a 5-4 loss to Baltimore on April 9 and had another good outing against the Orioles on Sunday, surrendering three earned runs with six strikeouts in seven innings. The Yankees (41-37), though, couldn't do much against Chris Tillman and had four hits in an 8-0 loss.
"He's some kind of pitcher," Orioles manager Buck Showalter said of Tanaka. "We were fortunate to catch him on a day when he wasn't as sharp as he normally is."
Now the Red Sox (36-44) can take their own crack at capitalizing on a second look at Tanaka, who leads the AL in ERA and has pitched at least six innings with no more than three earned runs allowed in each of his 15 starts.
Tanaka's fourth outing came against Boston on April 22 and he was outstanding in a 9-3 victory, giving up two earned runs with seven strikeouts and no walks over 7 1-3 innings. Slugger David Ortiz struck out twice against him.
With a veteran lineup that also features Dustin Pedroia, Mike Napoli and A.J. Pierzynski, Boston's hitters will be looking to make adjustments against Tanaka.
The Red Sox, however, didn't fare well Friday against previously struggling hurler Vidal Nuno, who came off two poor outings to pitch two-hit ball into the sixth inning and lead New York to a 6-0 victory.
Ortiz, Pedroia, Napoli and Pierzynski combined to go 0 for 14, though shortstop Stephen Drew did snap an 0-for-29 skid with a double in the seventh.
"Again, the base hit with the guy in scoring position has been elusive," manager John Farrell said after the Red Sox went 0 for 4 in those situations.
Boston is batting .227 with runners in scoring position.
Kelly Johnson and Brett Gardner hit back-to-back homers in the fourth inning and Brian McCann added a two-run shot in the eighth for the Yankees.
Looking to shut down New York's hitters in the middle game of this series will be Jon Lester (8-7, 3.14 ERA), who is 12-6 with a 3.96 ERA in his career against the Yankees but was roughed up a bit pitching opposite Tanaka on April 22.
Lester lasted only 4 2-3 innings in that outing at Fenway Park, allowing eight runs - three earned - and 11 hits with four walks.
The left-hander been much better over his last three starts, going 2-0 with a 1.66 ERA.