FORT WORTH, Texas -- Oklahoma State rode the left arm of Michael Freeman and a big third inning at the plate to a 7-2 victory against top-ranked TCU on Sunday at Lupton Stadium as the 23rd-ranked Cowboys earned a series win against the Frogs.

Freeman was masterful as the senior southpaw tossed his first-career complete game, striking out nine -- one shy of his career high -- and allowing just one earned run in a 127-pitch effort.

The Cowboys improved to 16-7 and are 2-1 after their opening weekend of Big 12 Conference play. Oklahoma State provided Freeman all the run support he needed with a two-out, six-run rally in the third inning.

"It's good to know that what I can do is working and that I can go a complete game, that my stuff is good enough to beat guys that are supposed to be the number one team in the nation," said Freeman, who improved to 4-0 on the season. "There's pressure in a rubber game, but you try and treat it like just another game and try not to let those outside thoughts have too much of an effect on you. You just play a pitch at a time and do what I know and let the guys work behind me, and they really did an awesome job."

In the game's pivotal third inning, TCU starter Alex Young, who entered the game with a 4-0 record and a 1.33 ERA, quickly retired OSU's first two hitters.

But a Gage Green single jump started what proved to be a huge two-out rally. Following Green's hit, Costello reached on an error and Dustin Williams walked to load the bases. Up next, Corey Hassel ripped a double down the left field line that cleared the bases and gave OSU a 3-0 lead.

Hassel's double was the first of four consecutive hits for the Cowboys. Jon Littell followed it with a single, and David Petrino then brought home OSU's fourth run with an infield single.

The Pokes weren't done as Jacob Chappell smacked a two-RBI double to left field that gave OSU a 6-0 lead and drove Young out of the game.

With the big lead, Freeman continued to fluster the TCU hitters as he allowed just two hits in the first six innings.

The Horned Frogs (17-4, 4-2) finally got on the scoreboard in the seventh, plating an unearned run on an RBI infield single by Nolan Brown.

Both teams scored their final runs in the eighth, with Donnie Walton picking up an RBI on his first hit of the season, a two-out single that made the score 7-1, before TCU pulled to within five in the bottom of the inning.

Along with Freeman, Hassel had a career day, tying a career high with three hits while recording a career-best three RBIs as OSU began defense of its 2014 Big 12 title by winning its eighth consecutive league series.