ARLINGTON -- The Rangers hoped for big things from outfielder Josh Hamilton this season, but the reality was they just didn't know.

His wealth of raw power and talent was apparent even to the untrained eye, and his Spring Training batting practice sessions became must-see stuff. But uncertainty lingered, not so much because of the former No. 1 Draft pick's dark history of addiction, but more pragmatically because he was entering his 10th year as a professional ballplayer with only 90 career games and 47 RBIs as a Major Leaguer under his belt.

Consider the Hamilton trade a success, even if pitcher Edinson Volquez started 4-0 for the Reds. Hamilton, whom Rangers general manager Jon Daniels acquired for the previously erratic right-hander, finished an even bigger April with the promise of a monster season to come.

Hamilton's first career grand slam started the Rangers on Wednesday toward an 11-9 victory over the Royals, and it capped in style one of the best run-producing months of April in Rangers history. The home run gave Hamilton an April RBI total to match his uniform number -- 32 -- which ranks second in club history only to the 35-RBI April recorded by Juan Gonzalez in 1998.

"It was all right," Hamilton deadpanned when asked to assess his first month with Texas.

It was a bit better than that. April ended with Hamilton leading the Major Leagues in RBIs, tied for second in the American League in home runs (six) and ranked third in the league in batting average (.330). The early Triple Crown candidate has been a fearsome force at home (.358-4-19) and on the road (.306-2-13).

"It doesn't matter what ballpark he hits in," Rangers second baseman Ian Kinsler said. "He's an animal."

As much as the Rangers struggled at times during their 10-18 April, Hamilton was been one of the consistent bright spots. One shudders to think where they might be without him.

"He's done everything you can possibly do," Rangers manager Ron Washington said. "He's played defense, he's thrown and run well, he hits, he drives in runs -- you couldn't ask for more."

Consider that of the 130 runs the Rangers managed to score in the first month, Hamilton drove in 24.6 percent of them.

"He's certainly been our RBI deliverer," Washington said. "He's been like the mailman."

Turning serious, Hamilton was quick to credit teammates for getting on base ahead of him and the team's training staff for helping work him into playing shape before and after games. He has never played more than 96 games in a season at any level, but he said he feels strong and healthy, helped by Washington's decision to use him as the designated hitter on Wednesday.

"I don't think I've really realized what I've done," Hamilton said. "I've never played a full season before, so the main thing for me has just been to do what I have to do before the games to get ready. But I feel good. It's been a while since I [was a designated hitter], and I don't like it. It's hard to stay in the game [mentally]. But it was good for my legs to have a day off."

Hamilton had plenty of offensive help on an extremely windy night in North Texas, and the Rangers needed every bit of it. Milton Bradley, David Murphy, Brandon Boggs and Gerald Laird each homered for the Rangers, who raced to leads of 7-0 after two innings and 9-1 after five.

"I never thought it was an easy or comfortable night, the way that wind was blowing," Washington said. "There wasn't any pitching that could stop anything."

Washington's concerns were well-founded. The Royals arose with eight runs in the final three innings, putting the potential tying run on deck after John Buck's two-run homer off closer C.J. Wilson in the top of the ninth. Wilson managed to retire Tony Pena Jr. and Joey Gathright to end the game.

Rangers starter Kevin Millwood (2-2) seemed to have things under control, holding the Royals to one run on four hits through six innings. But in a 12-pitch span of the seventh, he gave up an RBI single to Gathright, a run-scoring grounder to Esteban German and a two-run homer to David DeJesus to see his 9-1 lead shrink to 9-5.

Kansas City capped its five-run seventh with Alex Gordon's RBI single off Frank Francisco to close to 9-6.

Laird's two-run homer in the bottom of the seventh boosted the lead back to five runs at 11-6. But two errors by Texas rookie third baseman German Duran led to another Royals score in the eighth before Buck's two-run shot off Wilson in the ninth. All told, the teams combined for seven home runs, and the Rangers matched their season-best total for runs in a game.

"That was the hardest I've seen the wind blow here, since I've been here at least," Millwood said. "A couple of times, it blew you off balance a little bit. But I think it was tougher for the position players. Balls hit up in the wind made it tough."

Thankfully for the Rangers, Hamilton did his damage early. His grand slam off Royals starter Brian Bannister (3-3) staked Millwood to a 7-0 lead after two innings, giving the right-hander sufficient breathing room on this blustery night.

Just another fine night's work for Hamilton in a first month full of them.

"I think everybody felt he was talented enough to do something like this," Millwood said. "You can't expect the guy to have 30 RBIs every month, but when it happens to a good guy like that, you feel good for him.

"He's been good at the plate, good in the outfield, good in the clubhouse. He's a nice guy to have around."