When the Boston Red Sox take the field on Tuesday to begin a three-game series against the Oakland Athletics, they'll do it with the peace of mind that comes with possessing the majors' largest division lead. The Red Sox, who entered the spring presumed to be the third- or fourth-best team in the American League East, instead lead the New York Yankees and Tampa Bay Rays by three games apiece, a product in part of winning four of their last five contests. 

While the season is too young to take its results at face value, mid-May is often when the re-evaluation process begins. Enough time has passed for team-level results to have an impact on the final standings. For example, the Red Sox's hot start (22-14, or a 99-win pace) means that playing .500 ball from here out would leave them with an 85-77 record. Four "banked" wins may not seem like much, but it can make the difference when a team is deciding what to do at the trade deadline, or when a team finds itself in a tight playoff race.

With that in mind, it's time to start asking: are the Red Sox a legitimate playoff contender? Here are three factors that lead us to believe the answer is yes.

1. Early season performance

We mentioned the "banked wins" concept above, but the Red Sox have other reasons to feel optimistic about their first 36 games. Run differential, or runs scored minus runs allowed, often holds greater predictive value in small samples than a team's win-loss record. 

The Red Sox, who have bested their opponents by 33 runs this season, have the second-best per-game run differential in the majors, trailing only the Chicago White Sox. The Red Sox rank first or second in the AL in batting average, on-base percentage, and slugging percentage, and lead the majors in runs scored. Their offensive potency can't be credited solely to Fenway Park's generous dimensions, either: they rank second in the majors in wRC+, or FanGraphs' park-adjusted offensive metric that properly weighs the value of getting on base.

It may be tempting to credit Boston's success to a lean schedule -- after all, the Red Sox are coming off a stretch that saw them play the Baltimore Orioles, Detroit Tigers, and Texas Rangers … or three probable last-place teams -- yet that isn't the case, according to Baseball Reference's calculations. Not only has Boston played a middle-of-the-road slate, but it has performed better against good teams. Entering Tuesday, the Red Sox had the majors' best winning percentage against clubs with at least a .500 record (10-5), whereas they're just 12-9 against losing teams.