Alvarez (27-4) worked behind his wrestling and left Pettis (18-4) little room to operate in the 155-pound fight, which co-headlined UFC Fight Night inside TD Garden. The win improved Alvarez to 2-1 in the UFC.
Judges Douglas Crosby and Bryan Miner awarded the bout to Alvarez, 29-28. Judge Ryan Shea saw it for 29-28 for Pettis. ESPN.com also scored the fight for Pettis 29-28.
A former Bellator MMA lightweight champion, Alvarez repeatedly shot into Pettis' hips over the course of three rounds. When he couldn't drive Pettis to the ground, he smothered him against the fence and restricted his movement.
Pettis, who fights out of Roufusport in Milwaukee, looked calm defending the takedowns. He went to his butt several times in the opening round, but always popped immediately back up and didn't allow Alvarez to score any offense. When he did have space, the former champion unloaded body kicks from the southpaw stance.
The body kicks turned to leg kicks in the second round, which appeared to have affect Alvarez' movement. The 32-year-old continued to relentlessly pursue takedowns, however, and landed a few good jabs when things were in the center of the cage.
Alvarez's most significant work on the ground came in the third, when he was finally able to move into Pettis' half-guard and land some punches.
"I don't think it was split," Alvarez said. "I don't know what went on there or who scored it for Pettis, but that guy must have been watching a different fight. I would've liked to have kept it standing a bit more just for myself. But the plan was to keep him up against the cage. He landed a few shots, but I didn't feel any power from him and I was able to dominate the fight. I beat Gilbert Melendez and he got two shots at the title, I beat Pettis and he used to have the title and was the No. 1 guy, I fought Cowboy and he got a title shot. I want it! I want the best guys the promotion has to offer. Put them in front of me and I'll beat them. I want my shot!"
Overall, Alvarez was credited with six total takedowns. Pettis landed more strikes however, 109-to-74 according to immediate stats by Fightmetric.
It marks back-to-back split decision wins for Alvarez. After dropping his UFC debut to Donald Cerrone via decision in September 2014, Alvarez has earned wins against Pettis and Gilbert Melendez. Pettis, who lost he 155-pound title to Rafael dos Anjos in March, suffers consecutive losses for the first time in his career.
"I'm pissed. I don't know what to say right now," a disappointed Pettis said.
Browne too much for Mitrione
Heavyweight Travis Browne (18-3-1) picked up his 14th career knockout against Matt Mitrione (9-5), finishing him with punches on the ground at 4 minutes, 9 seconds of the third round. The fight was somewhat controversial, in that Browne poked Mitrione in the eye twice. Referee Gary Foreman did not take a point from Browne and didn't appear to verbally warn him until after the second foul. The bout was close until the third, when Browne took Mitrione down, moved to mount and started to unload strikes. Mitrione, in addition to bad hematoma over his right eye, appeared to suffer an injury to his clavicle near the end of the fight. For Browne, it improves his UFC mark to 9-3.
"Patience," Browne said of his strategy to win. "I kept the distance and didn't try to pressure too much. I got on top and finished it. I want the championship and I won't settle for anything less."
Trinaldo outscores Pearson
Brazilian lightweight Francisco Trinaldo (19-4) earned a unanimous decision (30-27, 30-27, 29-28) over Ross Pearson (18-10) for his ninth win in the Octagon. Trinaldo lifted Pearson off the ground and slammed him on his head in the first round. He hurt him with knees in the second and a counter left hand. The 37-year-old started to tire a bit in the third, but still did enough to pitch a shutout on two of the three scorecards. Pearson drops to 10-7 in the UFC.
"That was my fifth win in a row and I know I'm 37, but the key to me getting better the older I get is my family, my friends and my team," Trinaldo said. "Ross is a very tough opponent and I had to listen to my corners very closely so that I could achieve a better result and win the fight. I'm going to go back to Brazil now and have another party for all of the kids in my neighborhood and all of their friends."
Said Pearson: "I think I pressured the fight, I controlled the distance and controlled the fight. He did land two good shots, but he never hurt me. I was never in danger."
Cote keeps winning
Welterweight Patrick Cote (23-9) continues to rack up wins at age 35, defeating Ben Saunders (19-7-2) by TKO at 1:14 of the second round. It finally improves Cote to a winning record in the UFC. He started his career in the Octagon 0-4. Cote, out of Quebec City, hurt Saunders with punches on the ground. Saunders did not protest the stoppage. Cote is now 6-1 in his past seven.
"Ben is a tall southpaw, so I knew my footwork would be important," Cote said. "I didn't push the pace enough in the first round, so when I got back to my corner they told me I needed to move forward more, push the pace and let my hands go. I didn't win Powerball, but I hope I get that bonus, I had a great performance tonight.
"I'm the only one left from old school Canadian MMA. It was me and Sam Stout, but now that he's retired it's just me and it's an honor to be the face of Canadian MMA right now. I want a top-15 opponent next; or there's a guy coming back in August, his name is Nick Diaz, let's do it Nick."
Herman finishes Boetsch in Round 2
Light heavyweight Ed Herman (23-11) put Tim Boetsch (18-10) away with strikes at 1:39 of the second round. The finish came after Herman, 35, dropped Boetsch with a knee out of the Thai clinch. It was Herman's first UFC fight at 205 pounds. Since his debut in 2006, Herman has fought exclusively at 185. He said the change is permanent. Boetsch, out of Lincolnville, Maine, suffers his third loss in a row. He has been knocked out in back-to-back fights.
"This is a permanent move to light heavyweight. I feel like I have a lot more energy and power in this division," Herman said after the win. "I saw a lot of openings in the first round to land the knee, he didn't have a lot of movement. I went back to my corner between rounds and they saw the same, so I knew going into the second round that's what I had to do. Who's the champion in this division? Daniel Cormier -- I want you next."
Felder submits Cruickshank
Lightweight Paul Felder (11-2) scored a submission win over Daron Cruickshank (16-8), locking in a rear-naked choke at 3:56 of the final round. Felder, out of Philadelphia, went into the third round tied with Cruickshank on two judges' scorecards and down 0-2 on the third. Ultimately it didn't matter, as Felder took Cruickshank down and transitioned to his back for the choke. He snaps a two-fight skid with the win.
"I know we're both high level strikers, but I wasn't surprised at all that I was able to finish with a choke," Felder said. "Coming into this camp Jafari, my wrestling coach and Daniel Gracie were key in helping me prepare and develop the game plan. We noticed that Daron had some weaknesses on the ground and I think that his last two losses were via rear naked choke. I knew his striking was on point and different; maybe even better than mine in some areas, so wrestling was always at the forefront of this camp. I want a top-15 opponent next."
Said Cruickshank: "I love the fans and love the support they've shown me. Thank you for believing in me through the ups and downs."