Soriano, the top minor leaguer in the Seattle Mariners' system, and Harden, a 21-year-old right-hander atop Oakland's list of prospects, didn't leave the 6,128 in attendance disappointed.
Soriano allowed only two hits and one run in eight innings to one-up Harden and lead Tacoma to a 3-1 win.
"His slider was working really well tonight," said Tacoma manager Dan Rohn of Soriano in the clubhouse after the game.
Harden gave up four hits and two runs in seven innings of work.
In the past, Soriano has often relied on getting batters out with his mid-90s fastball. That was the case in his previous outing, May 26th, when he stuck out 10 Tucson batters en route to a 5-2 victory.
Saturday, the well-composed Domincan did it with his two other plus-pitches - a hard-slider and a knee-buckling changeup. He worked ahead of the batters, throwing first-pitch strikes to 19 of the 26 he faced, and walked only one on the night.
But more importantly, Soriano kept runners off the basepaths. The Rivercats didn't record their first hit until Bobby Crosby laced a line-drive single up the middle to lead off the fourth inning.
Harden didn't fare much worse, however. He limited the Rainiers to two hits through the first five innings, both coming in the third inning. Harden retired Tacoma in order in the other innings - the first, second, fourth and fifth.
Finally, the Rainiers got to the future star in the sixth. With one out, Chad Meyers singled off the outstreched glove of first baseman David McCarty to bring up right fielder Kenny Kelly. Kelly promptly brought Meyers home with a triple that hit high off the wooden right field wall to make it 1-0.
Soriano appeared to be sailing along, having retired 12 Rivercats batters in a row after giving up the third inning hit to Crosby. But that came to an end in the eighth, when left fielder Mike Edwards hit a blast over the left field wall to knot the score at 1-1.
Seeing an opportunity to get the win, Harden headed back out on the field for the bottom half of the eighth. The plan backfired when he walked the leadoff batter that inning, Julio Mosquera, and was replaced by Roy Smith.
Tacoma scored twice before Smith could get out of the inning, the go-ahead run coming on a bases-loaded walk to Jalal Leach that scored Mosquera, Harden's runner.
"It was fun to watch - it was just a matter of time before somone made a mistake," said Rohn of the pitchers' duel. "Luckily for us, it was them."
Aaron Looper came on to close the game for Tacoma in the ninth, leaving Harden with the loss.
He fell to 5-2 on the year.