Real or Mirage: Which surprising May performances are here to stay?

One of the biggest joys in a baseball season is watching players break out and become stars, and seeing others enjoy fleeting moments on top of the mountain.

Less than two weeks into this season's second month, there are several players on both sides of the ball delivering at a surprising level. Let's take a look at six - three hitters and three pitchers - and try to determine whether this is their new normal, or if a fall is imminent.

*Stats in charts are from May 2018

Nomar Mazara, Rangers

This is the version of Mazara the Texas Rangers were hoping for when they brought him up as a 21-year-old in 2016. He hit the ground running in May of his rookie campaign, hitting seven home runs in 27 games. He's already matched that number in this month alone.

Obviously, we're dealing with small sample sizes for all of the players on this list, and 40 plate appearances for Mazara in May is not a lot. The power surge is nice, and that he's only 23 suggests perhaps he's turning a corner, but it's worth exercising a little bit of trepidation.

He's tearing the cover off the ball - 53.8 percent of contact has been hard this month, and 34.6 percent has resulted in a line drive - and even though the results haven't been there against lefties, he's seemingly making adjustments. Most of his contact against left-handed pitchers this month has been to opposite field or up the middle. His pull rate against righties is 63.2 percent. He's going with the pitch he's given.

Again, it's a small sample, but if Mazara can continue to make adjustments against lefties, which has been the Achilles' heel in his young career, he can withstand any pressure that otherwise could have been mounting to turn him into a platoon bat.

Verdict: He's the real deal

Matt Adams, Nationals

We've been here before with Adams, kind of. When the St. Louis Cardinals dealt him to the Atlanta Braves in 2017, he saw a bit of a rejuvenation. From his Braves debut on May 21 through the end of June, he hit .294/.346/.615 with 12 home runs and 31 RBIs across 156 plate appearances.

The rest of the season, 158 plate appearances, he hit .250/.285/.473 with seven home runs and 27 RBIs. While that wasn't a catastrophic drop, it wasn't nearly the torrid pace he teased early on.

The biggest change in Adams' approach this season has been his refined plate discipline. He's swinging at only 46.4 percent of pitches, and only 32.7 percent of pitches outside the strike zone. Both are the lowest since his 108-game effort in 2013, which remains his most balanced season to date.

If Adams can continue to be patient - he's also posted a career-high 14 percent walk rate - he'll make his case to remain an everyday player once the outfield is fully healthy. And with how poorly Ryan Zimmerman has hit, Adams could be in line for the starting gig at first base. But we've seen false starts and surges before, so temper expectations for now.

Verdict: Don't bet the farm on this continuing

Eddie Rosario, Twins

Since the calendar turned to May, Rosario has been one of the toughest outs in the American League. He's batting .400 for the month, and 10 of his 16 hits have gone for extra bases.

By this point, you know what you have with Rosario - he swings the bat a ton. In 2017, he swung the eighth most among all qualified hitters. This season, only Javier Baez is swinging at more pitches.

The problem with Rosario is that he's never among the league leaders in contact rate, but he does make the most out of his contact. Basically, a stretch like this should never come as a surprise, but it also can't be a perfect representation of expectations going forward. In that same vein, when he slumps like he did in April (.231 batting average with 22 strikeouts), it shouldn't be seen as the norm, either.

Verdict: Expect fluctuations to continue

James Paxton, Mariners

All Paxton has done in May is strike out 16 batters in one game and throw a no-hitter in the next. No big deal. He hasn't allowed a run in 16 innings, and is making a case for himself as one of the best arms in the game.

Is it sustainable? In short, yes with an asterisk. Paxton's dominance this month is in line with his best stretches from 2017. He opened last season going 3-0 with a 1.43 ERA and 45 strikeouts in his first six starts. Then he hit the disabled list. From July 7 to Aug. 10, he was 6-0 with a 1.99 ERA and 56 strikeouts in 45 1/3 innings. Then he missed a month.

It's the story of Paxton's career - plenty of potential that's gone mostly unrealized due to an inability to stay on the field. It's the same story now. If Paxton can stay healthy, he's going to challenge for a Cy Young. But a few more months lost to injuries, and he'll be baseball's latest patron saint of missed opportunities.

Verdict: Elite going forward barring injuries

Matt Boyd, Tigers

Over the course of a relatively brief, and fairly tumultuous, pro career, Boyd has twice started a game and failed to record a single out. Expectations have, understandably, become muted.

And as good as he's been for the Tigers all season (his 2.01 FIP this month combined with a .342 BABIP even suggests the ERA could be somewhat unlucky), Boyd's probably not destined for a true breakout. For one, his 6.50 K/9 is his lowest rate to date. He doesn't miss enough bats to instill much confidence in his sustained success.

He's also reduced his home runs allowed without seeing a bump in ground-ball rate. Expect that 5.5 percent HR/FB rate to steadily rise unless Boyd continues to generate soft contact at a career-best pace (26.9 percent).

Verdict: A course correction is coming

Julio Teheran, Braves

Like Paxton, Teheran hasn't allowed a run in May. The biggest key to this success - other than playing the Rays and Mets - has been his command. Over his first four starts, across 20 innings, Teheran issues 17 walks. Since then, he's walked only five over 23 innings. Walks are a killer, and it's no coincidence that cutting down on the free passes has also helped extend his outings.

It's the story of his career. Teheran's BB/9 went from 1.96 in 2016 to 3.44 in 2017, and guess what happened? He had a much worse season. A similar change occurred from 2014 to 2015, when he went from 3.2 WAR to 1.1.

Teheran has been a staple of the Braves' rotation for what seems like forever (but he's still only 27), and he's been very effective in bursts. It seems like some of the shine has dulled, but his recent string of success shouldn't be seen as a temporary blip.

Verdict: He's back! (As long as he keeps the walks down)

(Photos courtesy: Getty Images)