Rowdy Tellez broke out as one of the game's better first-base prospects with 23 homers and a .917 OPS as a 21-year-old in Double-A in 2016, but he produced a total of just 19 homers with a .692 OPS during the next two seasons in Triple-A. Nevertheless, the Blue Jays called him up on Sept. 4 to get a glimpse of how he might fit in their future.
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Since then, Tellez (No. 28 on the Blue Jays Top 30) has been Toronto's best hitter. He became the first player in the live-ball era to deliver extra-base hits in each of his three plate appearances, and he's batting .385/.400/.744 with a pair of home runs through 40 trips to the plate. It's a small sample size and he has been used mostly in a platoon role facing right-handers, but he definitely has boosted his prospect status.
Signed for a well above-slot $850,000 as a 30th-rounder in 2013, Tellez is the 12th big leaguer to come out of Elk Grove (Calif.) High, also the alma mater of J.D. Davis, David Freitas, David Hernandez and the No. 4 overall pick in this year's Draft, Nick Madrigal. He offers an intriguing combination of left-handed power potential and plate discipline, even if his home run numbers dropped the last two years.
Toronto doesn't have an obvious opening for Tellez in its 2019 lineup, so he may have to swallow some more time in Triple-A. The Jays' two best hitters this season have been Justin Smoak and Kendrys Morales, who occupy the two positions (first base and DH) that Tellez can play and are both under contract for next year.

Even if his immediate future isn't clear, Tellez's present is spectacular. Here are four other September callups with notable performances:
Josh James, RHP, Astros
After leading the Minors in strikeout rate (13.5), the Astros No. 6 prospect has blown away hitters in the Majors as well. He has 24 strikeouts in 16 innings, along with a 2.81 ERA, a win in two starts and a pair of holds in two relief appearances. He has averaged 97 mph with his fastball and 86 mph with his slider, and it would behoove the Astros to find space on their postseason roster to include him.

Francisco Mejia, C, Padres
The top-rated catcher (No. 21 overall) on MLB Pipeline's Top 100 Prospects list, Mejia homered twice in his first start for the Padres, who acquired him from the Indians in July in exchange for Brad Hand and Adam Cimber. Curiously for a player who needs to polish his receiving and a team that needs to figure out if it would be better off making the most out of his bat by moving its No. 3 prospect to a less challenging position, he has started only five more games since behind the plate. He's hitting .242/.306/.545 with three homers in 36 plate appearances.

Sean Reid-Foley, RHP, Blue Jays
Toronto's No. 10 prospect has a pair of 10-strikeout efforts in three September starts, including one with five shutout innings against the Yankees, and a 3.86 ERA, 23 whiffs and a .186 opponent average in 16 2/3 innings this month. He works mainly with a low-90s fastball with life and a low-80s slider that has been absolutely filthy. According to FanGraphs, his slider has been worth 3.3 runs above average per 100 pitches -- which would make it the second-most valuable slider behind only Blake Snell's (3.8) if he had enough innings to qualify.

Christin Stewart, OF, Tigers
Stewart has slammed 83 homers in the Minors during the last three seasons, and he hit the first two of his big league career as part of a six-RBI night against the Royals. The Tigers' No. 6 prospect's penchant for drawing walks also has translated, as he has six in 46 plate appearances while batting .256/.370/.436. He should be a regular part of the Tigers' 2019 lineup as a left fielder/DH.