This week marked the highly anticipated return of Cardinals top prospect Alex Reyes (No. 16 overall), who took the mound Wednesday against the Brewers in his first game action since Tommy John surgery wiped out his 2017 season.
After dominating in four rehab starts at four different levels, the 23-year-old right-hander was solid in his season debut, allowing three hits and two walks while striking out a pair in four scoreless innings. Unfortunately for both St. Louis and fantasy owners alike, a dip in velocity during Reyes' final two frames and a visit from the team's training staff fueled speculation about a possible injury, and that notion was confirmed the following day when the Cardinals placed Reyes on the 10-day disabled list with a significant right lat strain.
In other debut news, Indians No. 3 prospect Shane Bieber (No. 99 overall) received his first taste of the Majors on Thursday night -- also his 23rd birthday -- in a spot start against Minnesota. The right-hander cruised through the first three innings but scuffled as he turned over the Twins' lineup for a second and third time, ultimately allowing four earned runs on eight hits with one walk and six strikeouts in 5 2/3 innings.
Below are our updated rankings of the top 10 fantasy prospects presently in the Minors. As always, they're based solely on expected 2018 fantasy production in the big leagues, while our Top 100 reflects long-term value in all phases of the game.

1. Vladimir Guerrero Jr., 3B, Blue Jays' No. 1/No. 2 overall (Previous rank: 1)
Guerrero's on-base streak may have ended at 37 games this week, but the 19-year-old phenom is continuing to put up obscene numbers for Double-A New Hampshire. He batted .438/.480/.768 in May, while totaling nine home runs, 10 doubles and 28 RBIs in 29 games. Overall, Guerrero leads the Minors in both batting (.414) and RBIs (53) through 49 games, during which he's compiled 11 home runs and 18 doubles with a robust 1.155 OPS (.414/.464/.691). Though the Blue Jays don't seem intent on promoting Guerrero just yet due to the club's ongoing struggles and because Guerrero needs more time to hone his defensive skills at third base, the teenager has nothing left to prove in the Minors offensively and has a chance to be an elite big league hitter the moment he arrives.
2. Eloy Jimenez, OF, White Sox No. 1/No. 3 overall (Previous rank: 4)
Jimenez, 21, has been a model of consistency this season in his return to Double-A Birmingham despite missing roughly two weeks out of the gate with a pectoral strain. He extended his hitting streak to 10 games on Thursday with a three-run home run that pushed him into first place on the Southern League leaderboard with 10 homers (tied) and 39 RBIs. He's hitting .331/.373/.623 overall, with 24 extra-base hits in 38 games. As with Guerrero, Jimenez is superstar in the making and worth stashing in all formats ahead of his inevitable arrival.

3. Nick Senzel, 3B, Reds' No. 1/No. 6 overall (Previous rank: 5)
The Reds shut down Senzel for much of May after he experienced vertigo symptoms for the second time in as many seasons, but he returned to action for Triple-A Louisville on Tuesday and, after a pair of 0-fer games, went 1-for-4 with a double, two RBIs and steal on Thursday. The strong performances so far by third baseman Eugenio Suarez and second baseman Scooter Gennett gives the Reds the freedom to be patient with Senzel's development, but there will be little keeping the 22-year-old third baseman from the Majors once he's back on track in earnest.
4. Michael Kopech, RHP, White Sox No. 2/No. 9 overall (Previous rank: 6)
Kopech has allowed two or fewer earned runs in three straight starts for Triple-A Charlotte while racking up 24 strikeouts and permitting just nine hits over 18 innings in that span. Such performances more or less sum of Kopech's fantasy upside, though his eight walks in those three outings, as well as his 25 walks in 10 starts this season, underscore his need for better command. Having pitched to a 3.86 ERA with 68 strikeouts and a .198 opponents' average in 51 1/3 frames, the 22-year-old Kopech seems ticketed for a second-half debut.
5. Kyle Tucker, OF, Astros' No. 2/No. 15 overall (Previous rank: NR)
Tucker has made a relatively smooth transition at the Triple-A level, where he's produced a .274/.355/.458 batting line in 49 games. The 21-year-old outfielder has tallied seven home runs and 16 doubles in that span and four of each over his past 11 games. One of 10 Minor Leaguers to total at least 20 homers and 20 steals (25 HR/21 SB) in 2017, Tucker has the ability to contribute in all five offensive categories once he's promoted.

6. Willie Calhoun, OF, Rangers' No. 2/No. 46 overall (Previous rank: 7)
Calhoun bounced back from a rocky first month of the season (.229/.308/.365) to slash .303/.327/.413 with 10 extra-base hits in May while hitting safely in 21 of 28 games for Triple-A Round Rock. While the 23-year-old continues to be limited by his defense, Calhoun has the type of left-handed bat that could soon have him driving in runs from the heart of the Rangers' lineup.
7. Willy Adames, SS, Rays' No. 2/No. 21 overall (Previous rank: NR)
The 22-year-old shortstop has hit safely in four of six games for Triple-A Durham after a three-game stint in the big leagues last week in which he went 2-for-12 and hit a solo home run off Red Sox ace Chris Sale in his second Major League at-bat. Adames should be back for good during the second half of the season, perhaps sooner, should the Rays suffer a middle-infield injury or make a trade.

8. Austin Riley, 3B, Braves' No. 8/No. 74 overall (Previous rank: 8)
Riley might be more than five years younger than the average player in the International League, but the 21-year-old third baseman has held his own for Triple-A Gwinnett, hitting .302/.352/.458 with four homers and 18 RBIs in 24 games since his promotion from Double-A Mississippi. He's produced a .318 average and a .943 OPS with 10 homers in 50 games between the two levels, all the while showing improved plate discipline and better defense at the hot corner.
9. Christin Stewart, OF, Tigers' No. 10 (Previous rank: 9)
Stewart has long been on fantasy owners' radars thanks to his blend of power and patience. This year, however, the 24-year-old has cut down his strikeout rate without sacrificing any power en route to a vastly improved .281 average and an International League-leading 13 home runs through 50 games.
10. Kolby Allard, LHP, Braves' No. 6/No. 51 overall (Previous rank: No. 10)
Allard's strikeout rate has continued to dip in his first Triple-A campaign, but the 20-year-old lefty is nonetheless having a strong season, ranking among the International League leaders with a 2.00 ERA (second), 1.06 WHIP (tied, fourth) and 63 innings pitched (first).
Dropped out: Alex Reyes, RHP, Cardinals (No. 2); Ryan McMahon, 2B, Rockies (No. 3)