Prospects Vladimir Guerrero Jr., Peter Alonso knocking on door to major leagues

SURPRISE, Ariz. — One of the biggest questions as we look toward the 2019 MLB season is how big a role will the game's top prospects play on their parent clubs. 

Judging from their performances in the Arizona Fall League — and in the league's annual Fall Stars Game — third baseman Vladimir Guerrero Jr. of the Toronto Blue Jays and first baseman Peter Alonso of the New York Mets should open the season on a major-league roster. 

Both young players did some amazing things Saturday night at the annual showcase event, which was won by the West All-Stars 7-6 on a walk-off single by Kansas City Royals catcher Meibrys Viloria.

Guerrero, 19, flashed some of the skills that made him the unquestioned No. 1 prospect in the minors. In the fifth inning, he hit a double off the left field wall that had an exit velocity of 117 mph. 

To put it in perspective, a total of 11 hitters in the majors last season hit a ball with an exit velocity of 117 mph or higher. That's 11 players ... ALL SEASON.

It's almost comical how good Guerrero was last season. The son of the  2018 Hall of Famer hit a combined .381/.437/.636 with 20 home runs at four different minor league levels. Yet the Jays chose not to promote him to the majors. Looks like he's going to make that decision even more difficult this spring, especially since he's second in the AFL with a .393 average.

Guerrero also walked, reached on an error in the ninth and scored the tying run on a two-out triple by San Diego Padres outfielder Buddy Reed. 

Reed then scored the winning run on Viloria's single was named the game's MVP. 

Earlier in the game, it looked like Alonso might be a front-runner for the award. 

In his first at-bat, Alonso, 23, faced hard-throwing Blue Jays right-hander Nate Pearson — who lit up the ballpark radar gun by hitting 103 mph several times with his fastball, and topping out at 104.

(The skeptic might wonder if the gun could have been running a little hot in an effort to build up some buzz. However, one scout in attendance confirmed the 104 was indeed legit.)

Facing one of those 103 mph fastballs, Alonso turned the tables by belting a home run to center field that gave the East an early 1-0 lead.

Alonso wasn't just impressive with his bat. For the second day in a row, he also showed some slick glovework.

After Guerrero doubled in the fifth and moved to third on a bobbled throw from the outfield, the East squad brought in the infield in an effort to keep the run from scoring. The next batter, Cavan Biggio of the Jays, hit a scorcher that Alonso somehow managed to pick on the short hop and tag first before Guerrero could advance. 

Alonso made a similar play the day before at Scottsdale Stadium when he dove to snag a short hop and make it to the bag ahead of the runner. If the reason the Mets didn't call him up this season was because he needed to work on his defense, that excuse doesn't seem to fly anymore. 

The Mets with Alonso and the Blue Jays with Guerrero hold the keys to how much the top prospects will contribute in the majors this season. Their service time concerns were one of the major topics of discussion this weekend at the First Pitch Arizona conference put on by the folks at Baseball HQ.

In the early 2019 fantasy drafts this weekend, Guerrero was taken in the second round — right around No. 20 overall — despite not playing a day in the majors and not being guaranteed he'll be on the Blue Jays roster.

The prevailing opinion is he'll spend the first couple weeks in the minors so the Jays will have him under contract for an additional year, then promote him to take over the starting job at third base. He's certainly proved he has little left to accomplish by playing against minor league pitchers. 

The same can be said for Alonso, whose fielding was the most pleasant surprise for me this trip. His bat certainly looks like it will play in New York. 

The future certainly looks bright for these two rising stars.

(More on some of the other AFL prospects to come ...)

Follow Gardner on Twitter @SteveAGardner