Scherzer's worst start this year came back on Apr. 24 against the Royals. In that game, Scherzer gave up five runs in five innings, but the Tigers lit up Kansas City starter Wade Davis, and Scherzer walked away with his second win of the season. That was one of three starts Scherzer had prior to Saturday night that, to my eye, were performances that should have earned him a loss.
Consider the fact that, through Friday, the average American League team had scored 4.42 runs per game this season. It would stand to reason, then, that any time a pitcher has given up five or more runs in a game this season, he has he turned in a performance that should have resulted in a loss given neutral support from his lineup and bullpen. In addition to that Apr. 24 game, Scherzer also gave up five runs on May 15 against the Astros, though he pitched seven innings in that game. Indeed, the Tigers lost that game, but they tied it up in the sixth inning to give Scherzer a no-decision before the bullpen caved in the ninth.
Now consider the definition of a quality start, which is generally regarded as the demarcation between a good outing for a starting pitcher and a poor one. A quality start is one in which a pitcher pitches six or more innings and allows three or fewer earned runs. A bare minimum quality start results in an ERA of 4.50, which fits nicely against that league average of 4.42 runs per team per game in the AL this year, suggesting that anything shy of a quality start should result in a loss. I'll be kinder and say that a pitcher has to fall short of a quality start by any combination of runs and innings adding up to two to have clearly deserved a loss.
Well, in addition to the two games in which he allowed five runs (two runs away from quality start), he allowed four runs in five innings in his first start of the year against the Yankees on Apr. 6 (thats one inning shy and one run over, a total of two), but the Tigers touched up Phil Hughes and the Yankees' bullpen, and Scherzer got a win in that game as well.
So, per the above, Scherzer should have had three losses this season prior to Saturday night and, in fact, should have never been undefeated at any point this season.
What about Clemens in 1986? The average team scored 4.61 runs per game in the AL in 1986, close enough to this year's scoring level to use the same standard for a loss. Clemens allowed five runs in consecutive starts on May 14 and May 20 of that year, but picked up the win both times as the Red Sox pounded the Angels' bullpen in the former and the Twins' Frank Viola (6 runs, no outs) in the latter. So, by the above standard, Clemens should have been 5-2 before he ever got a chance to go 14-0. Both pitchers were having excellent seasons (Clemens won both the Cy Young and MVP awards that year), but both also benefited greatly from their powerful offenses, as Clemens got 6.26 runs of support per game that year and Scherzer, prior to Saturday night, got 6.13 in his first 18 starts this season.
With Scherzer's loss, the pitcher with the longest undefeated streak in baseball this season is injured Red Sox starter Clay Buchholz, who has been on the disabled list with a 9-0 record since early June. Buchholz, whom the Red Sox hope to have back by the end of the month, hasn't had a single start this season that qualified as a loss per my above standards, as his only non-quality start was an almost exact match for Scherzer's performance Saturday night (6 IP, 4 R).