KANSAS CITY, Mo. — Casper Wells knew a pretty good offensive night was underway when his Mariners teammates teased him about hitting for the cycle just two innings in.

When the 9-4 rout of the Kansas City Royals was complete, Wells had finished with only a three-run homer a in the first inning and a two-run triple in the second. But achieving a career-best five runs batted in before many among the Monday night crowd had settled into their seats set the tone for another night of slugging prowess by the Mariners on the road.

Additional home runs by previously struggling Justin Smoak and Dustin Ackley helped the Mariners to their biggest offensive eruption in nearly four weeks. Throw in a triple by Ichiro and double by Jesus Montero and the debate about whether to move the home fences in at Safeco Field just got enough fuel for another month.

"It was just nice from an offensive perspective," said Wells, whose home run set the stage for the biggest first inning on the road by Seattle in more than four years. "Just to get that going. It was just pretty comforting to get that start right away."

The sweltering game-time temperature of 95 degrees may have played a role in the way some balls were flying off Seattle bats. So did Royals starting pitcher Jonathan Sanchez, whose seasonlong struggles took a turn toward the putrid in a 50-pitch outing that saw him notch only four outs.

As for Wells, he continues to thrive as the Mariners get him into the lineup on a daily basis.

"It's allowed me to have a consistent approach, not do too much at the plate and be a little more relaxed," Wells said. "Just knowing that you'll get a chance to play, righties and lefties alike. I think it just made me really dial in to having a consistent mindset, a consistent approach at the plate. As opposed to before, when I was just playing against lefties."

Smoak added a two-run homer off Sanchez the first inning, igniting a firestorm of boos from the crowd of 16,697. The crowd went apoplectic on Sanchez in the second, when Wells lined a triple to the gap in right-center to make it 7-0.

Royals manager Ned Yost drew a partial standing ovation as he trotted to the mound to yank his pitcher, now 1-6 with a 7.76 earned-run average.

That was pretty much the game, even though Seattle left-hander Jason Vargas, becoming a hot topic on the trade front, helped keep the Royals in it by allowing two more home runs — the 24th and 25th of the season given up by Vargas, who leads the major leagues. One question mark for any team trading for Vargas is how effective he can be away from Safeco Field, where he's given up only six long balls compared to 19 on the road.

The way that Safeco appears to benefit pitchers like Vargas is often cited by those opposing any changes to Safeco Field's fences. For all the talk about how the colder weather and spacious confines of the ballpark keeps the Mariners' offense down, the numbers are low for Seattle's opponents who play there as well.

Seattle entered the game batting .256 with a .715 on-base-plus-slugging percentage (OPS) on the road compared to just a .196 average and .563 OPS at home. The road numbers will only climb after this game and came at a good time for both Ackley and Smoak, two young hitters fighting most of the season to gain any plate traction.

Ackley said his sixth-inning homer the opposite way to left-center and a line out in the eighth were the closest he's come to duplicating his batting practice swings in a long while.

Smoak's batting average had dipped to .199 coming into the game, but he didn't miss an early fastball from Sanchez.

"If I keep having good at-bats and keep squaring the ball up, it's only a matter of time before good things happen for you," he said.

And only a matter of time before the cries grow even louder for the Mariners' top brass to do more to help the team hit like this at home.

Geoff Baker: 206-464-8286 or gbaker@seattletimes.com. On Twitter @gbakermariners.