LaPorta hit a two-run homer in the third, then took an accidental elbow to the head in the bottom of the inning and later left the game as the Indians beat the Texas Rangers 9-3 on Monday night.
LaPorta's homer helped the Indians to a 4-0 lead, but the Cleveland first baseman sustained a bruise on his head in the bottom half.
With Julio Borbon on first, Elvis Andrus hit a slow grounder and hustled down the line. Shortstop Jason Donald bounced his throw and Andrus' flying elbow hit LaPorta in the back of the head as Andrus ran past the base.
A dazed LaPorta fell on his back as the ball rolled into foul territory for a throwing error. Teammates were unable track down the ball in time to prevent Borbon from racing home to make it 4-1.
LaPorta was down for several minutes but remained in the game for the rest of the inning. He was replaced by Andy Marte in the fourth.
LaPorta was taken to a hospital for a precautionary CT scan. LaPorta suffered a concussion when he was hit in the head by a pitch while playing for Team USA in the 2008 Olympics, and the Indians didn't want to take any chances with one of their top young players.
"He was actually feeling nausea and he threw up a little bit too," Indians manager Manny Acta said. "It was a no-brainer to take him out of the game."
Nix, who was born in Dallas and lives there in the off-season, savored his second career two-homer game.
"It's a special night," said Nix, who had 15 family members and friends at the game. "It's great to be here at home and playing here. To be able to do that in front of them is special."
Texas slugger Nelson Cruz had a three-run homer wiped out after umpires watched a replay and correctly overturned the call. The AL-West leading Rangers have lost five of seven.
"We were playing catch-up all night and couldn't do it," Rangers manager Ron Washington said. "They just kept pouring runs."
Cleveland's Austin Kearns was hit by a pitch three times, by three different pitchers.
Indians reliever Chris Perez threw behind Andrus in the bottom of the eighth, and Andrus stared at the right-hander before striking out.
Cleveland starter Aaron Laffey was staked to a 6-2 lead, but was unable to get out of the fifth to qualify for the decision.
Joe Smith (1-1) allowed two hits in 1 2/3 innings of scoreless relief for his first major league victory.
Laffey gave up one earned and five hits in 4 1/3 innings before being pulled after throwing 101 pitches.
LaPorta and Santana homered off Omar Beltre (0-1) in the third inning of the rookie's second big league start, giving the Indians a 4-0 lead.
Beltre allowed four runs and four hits in three innings. He went four innings in his major league debut against the Los Angeles Angels on June 30.
Josh Hamilton extended his home hitting streak to 25 games, second-longest in club history, with a fourth-inning single. Al Oliver holds the home record with a 30-game streak in 1981.
The Rangers added a run in the sixth when home plate umpire Bob Davidson called a balk on Smith, scoring Bengie Molina from third to make it 7-3. Smith stepped off the rubber, then fired to first to pick off Borbon, but Davidson immediately called the balk.
Davidson also called a balk in the seventh on Texas' Pedro Strop.
"If Bob called it a balk, it must have been a balk," Washington said of the two calls.
Texas trailed 9-3 when Cruz lost his home run. The drive down the right-field line appeared to sail to the right of the foul pole, yet he circled the bases as the fans celebrated.
After the umpires reviewed the call and reversed it, Cruz returned to the batter's box and struck out.
"The first base umpire [Chris Guccione] thought it went around the pole," crew chief Tim Tschida said. "It started out so far fair that it kept coming around, and, when you're the guy on first, it flashes in front of the pole -- did it go around it or did it get it?
"The three of us were pretty sure that it was foul and never got it. We went and looked at the replay and made sure it didn't glance off the pole. And it didn't. I mean, it was close, it ended up being only three inches from it, or it looked like that."
Texas RHP Alexi Ogando hadn't allowed a run in the first 11 innings of his career until he gave up Nix's two-run homer in the seventh. ... Cleveland RF Shin-Soo Choo will have his sprained right thumb examined on Tuesday to determine if surgery is necessary. The Indians originally projected that Choo would be out for several weeks, and a timetable for his return will be set pending Tuesday's exam by Dr. Thomas Graham in Cleveland. ... Rangers 1B Justin Smoak snapped an 0-for-25 slump with a single in the sixth.