Reigns was triumphant in, at long last, ending the reign of Universal Champion Brock Lesnar after over 500 days. Their long feud reached its climax in a brief but hard-hitting match that saw a vocal New York crowd show their displeasure with neither combatant carrying any real popularity amongst one of WWE's more vociferous audiences.
Rousey, meanwhile, is the new Raw Women's champion after she toppled Alexa Bliss in just four minutes to pick up her first championship since swapping UFC for WWE.
The swift nature of those bouts summed up a curious second half of the show that saw matches seemingly more rushed than the first portion of the event that had the 16,000 crowd hooked.
The WWE Championship match, hotly-anticipated between AJ Styles and challenger Samoa Joe, ended in a disqualification. Joe would have his hand raised, but champion Styles kept hold of his gold after being disqualified after he took exception to comments made by Joe to his family at ringside at the climax of a bout that delivered on its high expectations.
In response, Joe was decimated by Styles with a steel chair after the bloodied champion had finally heard enough.
Daniel Bryan's long-awaited match with The Miz ended in disappointment after Miz claimed an old-school, roguish victory with the help of some brass knuckles. Without a doubt, these two will tangle again, but it was enough to whet the appetite as Bryan continues to slowly edge back to his best.
Finn Balor, in the guise of the Demon, made short work of Baron Corbin while Shinsuke Nakamura successfully defended his US Championship over Jeff Hardy thanks in part to a sickening landing for Hardy on the apron of the ring near the end of the match.
The night had got off to a blistering start as Seth Rollins became a two-time Intercontinental champion by beating Dolph Ziggler.
With former Shield brother Dean Ambrose at ringside to deal with Ziggler's hired help Drew McIntyre, arguably the best performer in WWE at the moment was able to capitalise and, with a curb stomp, pin the Show Off for a decisive victory.
Kevin Owens had a night to forget as he was swiftly brushed aside by Braun Strowman, while The New Day had to make do with a disqualification win over The Bludgeon Brothers.
There is a new Smackdown Women's Champion after the recently-returning Charlotte Flair overcame Carmella and her own best friend Becky Lynch in a fantastic triple-threat bout – with Lynch shockingly turning on Flair after the match as frustrations boiled over.
WWE SummerSlam 2018 results:
Roman Reigns DEF. Brock Lesnar - New Universal champion
Ronda Rousey DEF. Alexa Bliss - New Raw Women's Champion
Samoa Joe DEF. WWE Champion AJ Styles by disqualification
Seth Rollins DEF. Dolph Ziggler - New Intercontinental champion
Finn Balor DEF. Baron Corbin
The Miz. DEF. Daniel Bryan
US Champion Shinsuke Nakamura DEF. Jeff Hardy
The New Day DEF. Smackdown tag team champions The Bludgeon Brothers by disqualification
Braun Strowman DEF. Kevin Owens
Charlotte Flair DEF. Carmell and Becky Lynch - New Smackdown Women's Champion
Raw tag team champions The B Team DEF. The Revival
Andrade 'Cien' Almas & Zelina Vega DEF. Rusev and Lana
WWE Cruiserweight champion Cedric Alexander DEF. Drew Gulak
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