SEATTLE -- Mariners second baseman Jose Lopez was listening to his car radio on Friday when he heard that his double-play partner for the past four seasons had been traded.

"I said, 'What?' " he recounted.

Speculation that started on Thursday night when shortstop Yuniesky Betancourt was held out of his second rehab game at Triple-A Tacoma became reality several hours later when the Mariners announced that they traded Betancourt to the Royals for two Minor League pitchers -- right-hander Danny Cortes and left-hander Derrick Saito.

"We talked about this back in November, the ability for [general manager Jack Zduriencik] to be able to acquire depth in our Minor League system as we move forward is paramount," manager Don Wakamatsu said. "This trade is part of that. This allows us to add arms, and one of those arms is not that far away."

That would be Cortes, the Royals' Minor League Pitcher of the Year in 2008 and rated as the organization's top pitching prospect entering the '09 season by Baseball America. The publication also rated the 22-year-old right-hander as the second-best prospect in the Royals system, as well as naming him as the owner of the system's best fastball and curveball.

He posted a 6-2 record in his past 11 outings (10 starts) after losing his first four decisions this season. He will report to the Mariners' Double-A team, West Tennessee.

The 6-foot-6, 216-pounder from Pomona, Calif., was originally selected by the White Sox in the seventh round of the First-Year Player Draft in 2005. He was traded to the Royals on July 24, 2006.

The 21-year-old Saito had a 2-6 record, 4.26 ERA and one save for Class A Burlington this season. He also started the season slowly, surrendering eight earned runs in his first four outings but just 16 runs over his past 42 1/3 innings.

He will report to Class-A Clinton.

"Acquiring talent is your first priority," Zduriencik said. "Sometimes it's in the way of arms and other times it may be a position player. At the end of the day, everybody needs more arms. You never have enough arms."

Zduriencik said the deal took the past two days to finalize and was further fueled by the success Ronny Cedeno has had since replacing Betancourt, who suffered a strained left hamstring on June 24.

"I don't want to talk negative about any player," Zduriencik said when asked if Betancourt's unwillingness to make adjustments soured the organization him. "It just got to point where we were really happy with what Ronny was doing out there.

"We're very happy with his defense. We're hoping that [offense] comes around a little bit. It was just time to move on.

"We got a couple nice arms. When you have a chance to get someone's Minor League Player of the Year, I think you have to weigh everything. At this moment in time, we think this is the right thing to do."

Cedeno has played shortstop superbly, but went into Friday night's game against the Rangers with a .149 batting average, four home runs and 13 RBIs.

"Ronny has hit in the past, and on this last road trip he hit a couple of big home runs for us," Wakamatsu said. "We know the potential is there offensively and it's up to us to give him the at-bats he needs to get to that point."

Wakamatsu said the trade could have the same effect on Cedeno that Russell Branyan has had since signing as a free agent. He was anointed as the first baseman, the organization has stuck to its promise, and Branyan is having a career year.

"You have heard Russell speak about it since day one of Spring Training that he never really had an opportunity to be a starter," Wakamatsu said. "Ronny came into Spring Training competing for a job and now it's his. I would like to think he feels a lot more comfortable knowing that he has a supporting cast around him."

Betancourt spent a few hours at Safeco Field on Friday, packing his gear and saying goodbye.

"It is just part of the game," he said through an interpreter. "Trades happen. If it was supposed to happen, it's going to happen. But it is sad to leave the city that I've been in the past four years, my teammates and the front-office executives. It is sad to leave all the people here in Seattle."

Betancourt said he would report to the Royals' Double-A farm team to continue his rehab program and join the big league club following next week's All-Star break.

"It's a good thing for him," Lopez said. "I think he will get to play more there than he would here."

"He was good for the organization and I will miss him," All-Star pitcher Felix Hernandez said.

Several minutes later, while Betancourt was being interviewed, Hernandez walked past the group and told his former teammate the sequence of pitches he would be getting the first time they face each other.

He was joking and Betancourt was smiling.