CARSON, California – Fernando Martinez proved his superiority over Jerwin Ancajas again Saturday night.

The rugged, aggressive Argentinean battered the former IBF junior bantamweight champion for much of their immediate rematch. Martinez retained the IBF belt he won from the Filipino southpaw February 26 by winning a 12-round unanimous decision in the opener of a “Showtime Championship Boxing” tripleheader from Dignity Health Sports Park.

Judges Tiffany Clinton (118-110), Ellis Johnson (119-109) and Zachary Young (118-110) all declared Martinez a clear winner.

Martinez (15-0, 8 KOs) successfully defended the IBF 115-pound championship he won from Ancajas 7½ months ago in Las Vegas. Ancajas (33-3-2, 22 KOs) was a 5-1 favorite entering their first bout and the second longest-reigning champion in boxing, but Martinez’s decisive victory February 26 made him almost a 3-1 favorite before their rematch.

A contractual clause obligated Martinez to grant Ancajas an immediate rematch, but Martinez handled him with relative ease again.

The gutsy Ancajas clearly needed a knockout by the time the 12th round began. He traded with Martinez, who took Ancajas’ cleanest shots without incident and landed hard punches of his own over those final three minutes.

Barely a minute into the 12th round, Ancajas caught Martinez with a straight left hand. Martinez hammered him, however, with numerous flush shots in the final half of the last round.

A right hook by Ancajas connected with 1:05 into the 11th round, but it had little effect on Martinez. Toward the end of the 11th round, Martinez turned Ancajas’ head around with a right hand.

Ancajas connected with a left hand that made Martinez charge after him with a minute to go in the 10th round. Ancajas took less punishment in the round, but clearly was way behind on the scorecards by then.

Seemingly determined to avoid a stoppage by referee Eddie Hernandez Sr. or anyone in his corner, Ancajas connected with his fair share of punches in the ninth round. He just couldn’t stop Martinez from moving forward, not even after he clipped Martinez with a right hook toward the end of the ninth round.

Martinez responded to that shot by knocking Ancajas into the ropes with a right hand of his own.

Martinez continued to unloaded power punches on Ancajas during the eighth round. Ancajas’ chin held up well, but swelling became noticeable on his face at that point.

After rocking Ancajas toward the end of the sixth round, Martinez got off to a strong start by blasting Ancajas with a flurry of flush punches early in the seventh round. Ancajas hit Martinez with a low blow, which gave him a brief break, but Martinez was just as aggressive once he recovered.

An accidental clash of heads later opened a cut between Ancajas’ eyes, which caused a commission doctor to look at him with 44 seconds to go in the seventh round.

Martinez hammered Ancajas with hard right hands and a left hook toward the end of the sixth round.

Less than 30 seconds into the fifth round, Ancajas caught Martinez with a straight left as Martinez came forward. Martinez later drilled Ancajas with a right hand that landed with just over 1:20 to go in the fifth round.

Ancajas cracked Martinez with a right hook, which made Martinez charge after him toward the end of the fifth round.

A lunging left by Martinez made Ancajas wince with about two minutes remaining in the fourth round. Ancajas cracked Martinez with a counter right hook just after the midway mark of the fourth round.

A straight left by Ancajas briefly backed up Ancajas with just over 30 seconds on the clock in the fourth round. Martinez then connected with a left hook and a right hand as Ancajas backed up against the ropes with under 20 seconds to go in the fourth round.

Martinez pressed Ancajas again in the third round. Ancajas attempted to hold Martinez and occasionally landed counter shots, but nothing that could keep Martinez from coming forward.

A determined Martinez landed numerous punches to Ancajas’ head and body during the final minute of the third round.

Ancajas held the hard-charging Martinez with about 10 seconds to go in the second round.

Ancajas caught Martinez with a combination with about two minutes to go in the second round, right after Martinez lost his balance. Earlier in the second round, Ancajas connected with a right uppercut that got Martinez’s attention.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.