Rob Van Dam def. United States Champion Dean Ambrose by disqualification (Kickoff Match)

LOS ANGELES – The Biggest Party of the Summer got off to a rousing – and controversial – start, as volatile United States Champion Dean Ambrose lost to Rob Van Dam by disqualification, but retained his star-spangled title in a contentious SummerSlam Kickoff Match.

Watch the SummerSlam Kickoff show | Check out photos of the U.S. Title Match

The back-and-forth battle – which streamed live on WWE.com, the WWE App, YouTube, Facebook, Yahoo!, Samsung SMART TVs, Sony PlayStation 3, Twitter, Google+, Pinterest and Pheed as part of the hour-long Kickoff show – featured the involvement of not only WWE Tag Team Champions Roman Reigns and Seth Rollins, but also Mark Henry and Big Show.

Van Dam’s high-octane style – which earned him No. 1 contendership with a victory in a  Raw 20-Man Battle Royal – and Ambrose’s technical wizardry were on display from the outset in front of a sold-out crowd inside Los Angeles’ STAPLES Center.  After a feeling-out process, the “Hound of Justice” took control with his distinctive offense, grounding his high-flying No. 1 contender and turning the match into a gritty brawl. Utilizing elbows, knees and a stinging neckbreaker, the U.S. Champion taunted the WWE fan-favorite as he attempted several pinfalls.

"Mr. Pay-Per-View," however, proved that he was just as impressive and dangerous, dazing his black-clad opponent with a series of acrobatic kicks. Showing tremendous physical and strategic flexibility, RVD turned a Rolling Thunder attempt into a beautiful crossbody, bringing the WWE Universe to its feet.

After missing a split-legged moonsault, the former WWE Champion nailed Rolling Thunder and was ready to close out the victory with his rib-rattling Five-Star Frog Splash. That is, until the WWE tag Team Champions, Reigns and Rollins, crashed the party, giving Ambrose the distraction he needed to escape the ring.

Before the “Hounds of Justice” could team-up on RVD, however, the challenger got some super-sized back-up of his own, as Mark Henry and Big Show, came out to even the odds.

The massive presence of The World’s Strongest Man and The World’s Largest Athlete helped immediately. When Ambrose tossed RVD from the ring, the behemoths kept Reigns and Rollins from attacking at ringside, giving him an opening to hit Ambrose with an amazing spinning kick off the apron.

As the momentum swung back and forth in the wildly exciting match, a distraction from Rollins nearly led to another pinfall by Ambrose, but RVD kicked out and kept the pressure on. Hitting Rolling Thunder again and following with the devastating Five-Star Frog Splash, he had the U.S. Champion all but finished. Then, out of nowhere, Reigns stormed the ring and nailed RVD with a massive Spear, giving him the disqualification victory, but not the U.S. Title.

After the controversial end to their battle, is a rematch with Ambrose in RVD’s immediate future? And could the WWE Tag Team Champions have some dangerous – and enormous – new adversaries in Henry and Big Show? No matter what unfolds, it’s hard to claim that “justice” was served in the SummerSlam Kickoff Match.