Who reigns supreme at junior middleweight? It's anyone's guess

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Alvarez stuns Seals with huge punch in Round 5 (0:24)

Eleider Alvarez forces Michael Seals to stumble backwards after connecting with a huge punch late in Round 5. For more Top Rank Boxing, sign up here for ESPN+ https://plus.espn.com/. (0:24)

PHILADELPHIA -- The junior middleweight division is as fun, interesting and unpredictable as any in boxing.

This time it was unheralded Dominican Jeison Rosario who turned the 154-pound weight class on its head with his wholly unexpected fifth-round knockout of Julian "J Rock" Williams in what had been a very competitive action fight. Rosario, 24, won the unified belts (IBF/WBA) on Saturday night at Temple University's Liacouras Center.

Williams (27-2-1, 16 KOs), 29, was heavily favored in his first defense, but Rosario looked as good as he ever has and spoiled the champion's homecoming.

Undoubtedly, a big reason for Rosario's success was because he went away for an extended training camp for the first time in his career.

"As soon as I stepped into the ring, I knew he could not hurt me," Rosario said. "I knew that my power was affecting him right away. This is a big victory for me and for the whole Dominican Republic. I have to give a lot of credit to my team. I had a 16-week training camp and that prepared me for this. My life is changed forever and I can support my family in a whole new way."

It was just last May that Williams upset the division's apple cart the same way Rosario (20-1-1, 14 KOs) did. That was when Williams went to Jarrett Hurd's home region in Fairfax, Virginia, and outpointed him in a very exciting action fight to take the two belts. The entire division is like that right now, with the various belts being passed around among several quality fighters with nobody really able to separate themselves from the pack.

There is Jermell Charlo, who lost his belt by controversial decision to Tony Harrison in December 2018 and then stopped him in the 11th round of a rematch this past December to regain it. I view Charlo as No. 1 in the division because he also owns wins over Erickson Lubin and former titlist Austin Trout. He has looked pretty good, but it is not clear cut that he's the best in the pack.

Williams looked like the No. 1 guy after he beat Hurd, and now some might consider Rosario the top guy after his authoritative stoppage of Williams. Williams has vowed to trigger his contractual right to a rematch.

Then there's Hurd, who looked like something special when he knocked out Harrison to win a vacant title in 2017 and then stopped Trout, who had never previously been stopped, and edged division stalwart Erislandy Lara to unify belts in the 2018 fight of the year. But then he lost to Williams, pulled out of a planned rematch and will return from that loss on Saturday against Francisco Santana after changing trainers.

Harrison, Lara and Lubin remain in the mix, as does undefeated Brian Castano, who fought to a draw with Lara last March and in November scored a solid fifth-round knockout of Wale Omotoso. Castano is the mandatory challenger for the belt held by Patrick Teixeira, who won a vacant strap in November in a terrific battle with Carlos Adames.

The great thing about the division is that virtually all of the players at 154 are aligned with Premier Boxing Champions, which made most of the previously mentioned fights and can continue to mix and match these guys in bouts that figure to be fun, interesting and unpredictable.

Eleider Alvarez back in the title hunt

Former light heavyweight world titlist Eleider "Storm" Alvarez reinserted himself into the title hunt in a big way with a sensational one-punch knockout of Michael Seals in the seventh round on Saturday night in the main event of the Top Rank Boxing on ESPN card at the Turning Stone Resort Casino in Verona, New York.

After a slow-paced fight, Alvarez (25-1, 13 KOs) turned out the lights with an overhand right that nailed Seals on the chin. The punch landed before the right hand Seals (24-3, 18 KOs) was throwing at the same time. Seals went down hard, the back if his head crashing into the bottom ring rope. Referee Danny Schiavone waved it off at 3 minutes without bothering to finish the count.

"During training camp, we practiced (the right hand) over and over," Alvarez said. "My trainer was mad at me at first because I wasn't doing what he was asking. Finally, we got the knockout. I was out of the ring for 11 months. I wanted to come back as the fighter that beat [Sergey] Kovalev, and this is what we practiced for."

Indeed, Alvarez had upset Kovalev to win a world title by seventh-round knockout in August 2018 before losing to him via one-sided decision in a rematch last February.

The next step: A week earlier in the Top Rank Boxing on ESPN main event, light heavyweight Joe Smith outpointed Jesse Hart in a fight between contenders. Afterward, Top Rank chairman Bob Arum, who has options on Smith, and Joe DeGuardia, Smith's promoter, both said they were interested in matching Smith with the Alvarez-Seals winner. If that very attractive bout happens, the winner will undoubtedly deserve a world title shot in a division in which Top Rank promotes unified world champion Artur Beterbiev. Beterbiev has a fight lined up in March, but will be open for business after that if he wins.

Fights you might have missed

Friday at Sloan, Iowa

Super middleweight Vladimir Shishkin (10-0, 6 KOs) UD Ulises Sierra, scores: 100-90, 99-91 (twice)

Shishkin cruised to a one-sided decision over Sierra in the main event of the 250th edition of Showtime's prospect-launching series "ShoBox: The Generation," which debuted in July 2001 and is still going strong. Shishkin, 28, a Russian native fighting out of Detroit, where he is trained by Sugarhill Steward - the nephew of the late Hall of Fame trainer Emanuel Steward and now Tyson Fury's trainer - said he fought despite an injured left biceps and elbow with hopes he could land a title shot. Sierra, who has sparred with fighters such as Canelo Alvarez and Andre Ward, became the 189th boxer to lose his undefeated record on "ShoBox."

Junior welterweights Shohjahon Ergashev (18-0, 16 KOs) KO1 Adrian Estrella (29-5, 24 KOs)

Ergashev, 28, an Uzbekistan native fighting out of Detroit, had a surprisingly easy time with Estrella in an impressive knockout. Ergashev, a southpaw, who is also trained by Steward, needed just a single left hand to the liver and 92 seconds to drill Estrella for the knockout. He went down writhing in pain and referee Paul Parry counted him out. Estrella, 29, of Fort Worth, Texas, who has trained with former junior welterweight titlist Regis Prograis, lost his second fight in a row.

Bantamweights Ja'Rico O'Quinn (14-0-1, 8 KOs) W8 Oscar Vasquez (15-3-1, 3 KOs), scores: 79-73 (three times)

O'Quinn, 24, of Detroit, a former amateur standout, who works a construction job to make ends meet, made his "ShoBox" debut and outfought Vasquez, 32, of Reno, Nevada. O'Quinn, who is also trained by Steward, lost the opening round and then swept the rest of the fight though many rounds were competitive. He did very effective work to the body, landing 83 overall, per CompuBox, compared to 40 for Vasquez, who dropped to 0-2-1 in his last three fights.