When the A’s dealt Yonder Alonso last month, their plan was to make Matt Olson the primary first baseman — and unlike Alonso, Oakland’s 2017 All-Star, Olson isn’t even platooning much. Olson started Sunday against Houston left-hander Dallas Keuchel, and the rookie entered Sunday’s finale against the Astros with a .250 average and .464 on-base percentage against lefties. “That’s an easy one right now,” manager Bob Melvin said of playing Olson every day. “He’s taken (Zach) Britton deep. It seems like he gets good swings against all lefties. … It’s tough to take him out of the lineup right now.” Olson homered off lefty Tony Sipp in the eighth Sunday. In 29 games since being recalled from Triple-A Nashville, Olson is batting .306 with 13 homers and 25 RBIs. Overall, he has 17 homers in just 149 at-bats. “Olson looks like the real deal,” said one scout who has followed Oakland all week. “I’ve been impressed with how he’s gotten on some pitches in the upper zone.” Olson’s 13 homers since Aug. 11 are the most in the AL. “I think he likes breaking balls right down the middle,” Houston manager A.J. Hinch said. “He doesn’t ever come off the powerful swing he has. ... He’s starting to handle left-handed pitching a little bit more and done some things that have shown some growth.” “I don’t look him in the eye anymore,” joked Ryon Healy , Olson’s roommate. “I’m scared of him now, what he’s able to do.”