With every opportunity to get their lineup rolling on Friday at Fenway Park, the Blue Jays were their own worst enemy with a string of baserunning errors in the 5-3 loss.

Aggression at the plate has often been Toronto’s downfall this season. In an effort to shake things up, manager Charlie Montoyo moved Cavan Biggio into the leadoff spot and slid his hottest hitter, Teoscar Hernández, all the way down to the No. 8 spot to stretch the lineup. Against Ryan Weber -- who entered with an 11.57 ERA and zero strikeouts through two starts -- the stage was set for a turnaround.

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To their credit, the Blue Jays looked better at the plate, but found other ways to push just a bit too hard. After Biggio hit a leadoff home run in the first and Bo Bichette advanced to second on a throwing error, Bichette ran into the first out of the inning at third base on a ground ball. Jump to the second inning, and Randal Grichuk was thrown out at second base as Travis Shaw swung through strike three. The next batter? Hernández, who doubled to left field.

“You should never make the first out at third base,” Montoyo said after the loss. “Or a ground ball at short, getting thrown out at third. You should never do that. Those were bad mistakes. We’re going to teach the kids to get better. It looks bigger when you’re not scoring runs.”

They weren’t done there, either. In the sixth, Vladimir Guerrero Jr. doubled home Rowdy Tellez to pull Toronto within one, but instead of staying on second with no outs and representing the tying run, Guerrero tried to advance to third on the relay home and was easily thrown out. The next batter? Grichuk, who singled off the Green Monster.

Guerrero also had a pair of defensive blunders in the seventh inning in foul territory. Xander Bogaerts popped up two consecutive balls near first base, both quite catchable, but Guerrero couldn’t bring in either one. The first, Guerrero overran coming in, and couldn’t adjust back in time. The second, Guerrero misjudged up against the netting and was far too shallow, his inexperience of playing the area around first base showing clearly. Bogaerts walked two pitches later.

Montoyo, who’s found the positives in every loss up to this point, was more pointed in his postgame comments this time around.

“He just missed them. There’s no excuse,” Montoyo said. “We’re in the big leagues and you should be able to make those plays. For some reason, he didn’t see them. He went too fast. When you go too fast, the ball moves a lot and I think that’s what happened. He was out of control when he went to it. He wasn’t going nice and easy.”

These outs are easier to stomach against an ace, but with Weber on the mound, it took the bats out of the Blue Jays’ hands and limited their opportunities to do damage before Boston turned to its bullpen.

This is where the dynamics of the Blue Jays’ roster comes in clearly. The club is trying to make an early push in the shortened 2020 season, while still developing its young core, like the 21-year-old Guerrero, on the fly. There will be bumps along the way, but those are suddenly playing out in what is already, essentially, a playoff race. There’s room for learning from nights like Friday, but one eye needs to be on competitiveness at all times.

“It’s player development in the big leagues,” Montoyo said. “We’re still young, but we cannot make those mistakes.”