BOSTON -- Plan A for the Red Sox on Sunday was for Brayan Bello to go deep into the game because the bullpen was, as manager Alex Cora put it, “A little short.”

Bello was good, but not great, and got 16 outs instead of the 21 or so the club would have preferred.

Sometimes you have to go to Plan B, and that’s exactly what the Red Sox did to edge out the Angels, 5-4, in the rubber match of a three-game series.

So what was Plan B?

It was one that entailed their most accomplished reliever, Kenley Jansen, retiring an all-time great with two outs in the top of the ninth and no margin for error. And for their reliever with the least amount of experience -- Rule 5 rookie Justin Slaten -- to get two of the biggest outs of the game on one pitch.

Let’s start with the final act of the drama, Jansen against Mike Trout with runners on second and third and two outs and Boston clinging to a one-run lead.

Though the jam Jansen found himself in was largely his doing thanks to a hit-by-pitch, a single and a walk, he found a way to get locked in when he needed to and blew a 94.3 mph cutter past the swing of Trout to end it. It was career save No. 424 for the big righty, tying him with John Franco for fifth on the all-time list behind Mariano Rivera (652), Trevor Hoffman (601), Lee Smith (478) and Francisco Rodríguez (437).

With first base open, Cora could have ordered up an intentional walk of Trout and nobody would have batted an eye. Instead, he had Jansen go after the superstar.

“It’s still Kenley Jansen,” said Cora. “I bet there were half a million out there who would walk Mike Trout, but this guy, he is fifth on the list of saves. [Trout] is one of the best players in the world, but we trust [Jansen].”

And with good reason -- Trout is now 1-for-12 lifetime against Jansen with nine strikeouts.

“He’s the best player in the game, still,” Jansen said. “I didn’t want my team to lose today. We’ve already been through a tough stretch. Got to find a way to get the best hitter out and win the series. That’s what my focus and goal was.”

The challenge brought out the best in Jansen.

“I love watching that man play, man. I don't think you're gonna see another player like that ever, in my opinion,” said Jansen. “Thank God I had great success against him, but it's fun watching him play. It’s always great to face the greats. I love facing guys like that.”

Now, let’s rewind to three innings earlier, which was the first time the game felt like it was hanging in the balance for the Red Sox.

Bello’s 107th pitch of the day yielded an infield single to Aaron Hicks that put runners on the corners with one out and the Red Sox clinging to a 3-2 lead.

To get out of that jam, Cora called on Slaten, who has been tremendous in the first couple of weeks of his career.

Slaten threw one pitch, a 90.7 mph cutter, and Brandon Drury hit into a 5-4-3 double play to end the frame.

“To be called on in that situation and know that we’ve got a chance to turn a double play, that was the only thing on my mind coming out of the bullpen,” Slaten said. “I just wanted to throw my best pitch and hope for a ground ball, and luckily I was able to throw one and get out of it. It felt good to pick up the team and to pick up Bello.”

Not only did Slaten pick up Bello in that sixth, but he picked up the entire bullpen by also navigating through the seventh and eighth to hand the ball to Jansen in the ninth. On a day Chris Martin was unavailable with a sore left shoulder, that was crucial.

While Rule 5 pickups can be hit or miss, Slaten has been nails (0.87 ERA, 0.39 WHIP, .094 opponents' batting average) in his first six MLB outings.

“He doesn’t get too emotional,” said Cora. “He gets the double play, and we’re really excited in the dugout and he is just like, ‘I have to go back in and get three more outs.’ He’s a good one. He is really good.”

And Jansen, who has been really good for a long time, made sure that Slaten’s clutch effort resulted in a win.