OAKLAND, Calif. -- Yoan Moncada thought he was headed straight to the major leagues when he signed a multimillion dollar deal with the Boston Red Sox on March 12 last year as an international free agent from Cuba.

Not so fast.

"Soon I realized that it's not that easy, so you have to go through the minors," Moncada said Friday. "I just stayed focused and did what I had to do and stayed the course."

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After playing 187 minor league games, Moncada was selected from Double-A Portland on Friday and made his major league debut, coming off the bench to play third base in the seventh inning of a 16-2 rout of the Oakland A's.

Moncada, 21, will make his first major league start Saturday at third base against the A's, Red Sox manager John Farrell said.

"He's an extremely athletic, exciting young player," Farrell said. "Has hit better from the left side of the plate. Has moved over to third base and handled the position well.

"I think a lot has been made of (only) eight or 10 games played at third base at Portland, but he's played a number of games at Cuba at third base before coming to the states. Now granted, this is a quicker pace, quicker level, but he wouldn't be here if we didn't feel he could step in and contribute."

In the seventh inning, Moncada made a nice backhand stop of a ground ball and strong throw to gun down A's second baseman Chad Pinder. At the plate, he walked in the eighth and scored from first on a double, showing his speed. He struck out in his final plate appearance.

"In a three-inning look, you see some exciting skills," Farrell said. "The fist play he gets is deep at third base and he makes a good, strong throw across the diamond. Scores on a double to right-center field where he ... runs through a stop sign, but you see the straight-away speed is outstanding. It was a glimpse, but he had a chance to show off two of the tools."

Moncada hit a combined .294 with six triples, 15 home runs and 62 RBIs and 45 stolen bases in 106 games for Class A Salem and Portland this year.

"I'm just looking to not to do too much, just play the same baseball that I've played in the time that's remaining," Moncada said. "I'm really just sticking to what I've done to get me to this point."

While Moncada makes his first major league start, Red Sox left-hander Rick Porcello will make his 236th career start and attempt to pick up his 19th win of the season. Porcello (18-3) leads the American League in victories. His previous career high for wins was 15 in 2014 with Detroit. He went 14-9 as a rookie for the Tigers in 2009 but was 9-15 with a 4.92 ERA last season, his first with Boston.

"Porcello's one of the best pitchers in the league this year," said Dave Dombrowski, Boston's president of baseball operations. "He's gone out there and given it to us on a consistent basis. ... This guy won 14 games as a 20-year-old, so he's always been a good pitcher.

"He's become a much better overall pitcher in the sense that he'll mix in his four-seamer when he needs to, mixes in the curveball a little bit more than he used to. So he's really got a good knack for pitching out there. He's very confident at this point and he's really pitched well for us."

The A's will counter with rookie right-hander Daniel Mengden, who will be recalled from Triple-A Nashville and make his 10th major league start. He's 1-5 with a 5.73 ERA for the A's. After being optioned to Nashville on July 26, Mengden went 5-1 with a 2.01 ERA in six starts for the Sounds.

"Good to get him back," A's manager Bob Melvin said. "He really got our attention early on. We felt like when we sent him down he was just a little bit tired, and they cut down on his workload. He's been pitching great since. It will be nice to have him back."