May is over and the service time clock is no longer much of an issue, so it’s time for clubs to start replacing some of the dead weight on their clubs with actual players with upside. In fact, some clubs have already started the process. Here’s a look, alphabetically, at some fantasy baseball prospects who should be owned as they are already in the majors or may be called up soon:

Dustin Ackley, 2B, Mariners: Ackley has steadily gotten better this season and actually has his average all the way up to .292 with seven homers and six steals. Ackley so far hasn’t put up big numbers in any category, yet he’s on the cusp of a call-up. The fact that he is so patient – he has 115 walks and just 112 strikeouts in the minors – is what the scouts love, and the Mariners believe he can hit for a little power and may use his speed (65 on the 20-80 scale) to steal plenty of bases as well.

Domonic Brown, OF, Phillies: He has a hit in all but three of the 10 games he has played in so far with Philadelphia and has four multi-hit games already. He has legitimate 20/20 tools right now and should get a chance to play nearly every day.

Aaron Crow, RP, Royals: He has risen to the role of closer in just 22 games in the majors. He has been pretty unhittable, giving up just four runs in 27 innings while striking out 26 and walking just nine. His fastball averages 95.3 mph mixed with a nasty slider and the occasional curveball too. Crow isn’t likely to remain the closer if Joakim established veteran Soria is healthy, but is an excellent pickup in case it is found that Soria has some kind of arm issue.

Desmond Jennings, OF, Rays: It seems like he’s been talked about for several years now, so shouldn’t he have been up here already? With Carl Crawford gone, he has a much clearer path to playing time, but the problem is that Matt Joyce is having a career year so far and Sam Fuld has stolen all his thunder. Truthfully, he hasn’t lit the world on fire the past two seasons, hitting .278 last year and only .268 this season, but his potential to get on base regularly and steal 40-plus bases and score tons of runs is something every fantasy team covets.

Brett Lawrie, 3B, Blue Jays: This guy is absolutely raking at Triple-A Las Vegas to the tune of .354/.415/.677 with 19 doubles, four triples, 15 HRs, 49 RBIs and even 11 SBs in 52 games. It’s fairly obvious he will be playing the hot corner for the Jays soon – reports even say he will make his debut Friday. When manager John Farrell was asked who he considered the Blue Jays’ everyday third baseman, he replied: “(Jayson) Nix, (John McDonald), Edwin (Encarnacion) – we’ve got three options there. And then, when Brett Lawrie comes, there’s another one.”

Jordan Lyles, SP, Astros: When Wandy Rodriguez went down, the 20-year-old was summoned and probably had the best debut of anyone this season. Lyles took a shutout into the eighth inning and ended up allowing just one earned run in seven innings, striking out four and walking none. The Astros have been aggressive with him (he was the only teenager in Triple-A last season), and it’s very possible he sticks around after Wandy comes back. He throws four pitches (fastball, curve, slider, changeup) for strikes and has been very durable, not missing a start in his three seasons. His time might be now.

Jesus Montero, C/DH, Yankees: Montero remains one of the best pure hitters in the minors and has a ton of power to go with the bat control, but he’s got two things against him right now: 1. He still may end up being mostly a DH, and 2. Barring injury, the Yankees don’t have a place for him right now unless they get rid of Jorge Posada. The other thing about Montero is that he isn’t lighting the world on fire, possibly because, as speculated, he may be bored. He has good reason to be, as he has already proven more than capable of lighting up minor-league pitching. His .782 OPS, four homers and just 14 extra-base hits aren’t exactly telling the Yankees there’s a rush. Our best guess here is that the Yankees trade him for pitching. Of course, they could literally call him up tomorrow too.

Mike Moustakas, 3B, Royals: If it seems like the Royals have an endless supply of prospects ready to come up, it’s because they do. Moustakas was thought to be ahead of Eric Hosmer coming into the season, but Hosmer earned the call by batting over .400 while Moustakas got out of the gate slowly. Moose has picked it up, though, and may be near a call-up of his own. The trick with the Royals is that they want these guys to stay around once they get to Kansas City. Moustakas’ ability to hit for power without sacrificing batting average makes him a potential annual All-Star.

Juan Nicasio, SP, Rockies: He got the call when Jorge de la Rosa went down with a season-ending elbow injury and won his debut, allowing just one unearned run in seven innings. The flamethrower (upper-90s fastball) will more than likely get an extended look and has a real chance of sticking in the rotation if his first start is any indication. He had a 63/10 K/BB ratio in the minors and if he can come close to that with the Rockies, he could be an asset to a fantasy roster.

Andrew Oliver, SP, Tigers: He held his own in his first start filling in for injured Phil Coke. He could get an extended look even after Coke returns, but a trip back to Triple-A may be more likely. He was a second-round pick in 2009 out of Oklahoma State and made five starts for the Tigers last season, getting knocked around a bit but still managing 18 Ks in 22 innings. This season, he is 4-3 with a 3.31 ERA in nine Triple-A starts. His lively fastball sits around 93-94 and tops out at about 96 and he has worked hard to incorporate his slider and curveball into the mix more often.

Anthony Rizzo, 1B, Padres: At the time of the Adrian Gonzalez trade, Rizzo wasn’t necessarily viewed as the centerpiece, but he has been nothing short of amazing this season in Triple-A. His statistics are not video game numbers (.366/.442/.720, 14 HRs, 56 RBIs in 42 games), but they really could be. He has had absolutely no trouble in the hitter-friendly Pacific Coast League, and considering he’s blocked by only the duo of Brad Hawpe (.233/.295/.346) and Jorge Cantu (.200/.244/.300), a call-up could be real soon.

Jemile Weeks, 2B, A’s: Given the position he plays and the fact that he is raking it at Triple-A, it seems likely the A’s will call him up soon. Rickie’s little brother is hitting .335 with six doubles, four triples, three homers and eight steals so far and could provide a spark that Mark Ellis and Andy LaRoche have yet to provide.