Terence Crawford earned the biggest win as well as biggest payday of his career following a ninth-round TKO win over Errol Spence Jr. in their welterweight title unification clash this past weekend. Crawford knocked Spence down three times before becoming the first undisputed and unified welterweight champion. He also cemented himself as the pound-for-pound best boxer in the world in the process. The question now is, what's next?

Spence revealed post-fight that he planned on activating his rematch clause and looks to be the most likely opponent for Crawford. However, a rematch — at least an immediate one — makes very little sense at this point. And so, given that Spence still has 30 days from the fight to make the rematch official, in the scenario that he chooses not to, here's a look at three alternate opponents Terence Crawford could fight next.

Jermell Charlo

This would arguably be the most popular option. Who doesn't want to see a fight between an undisputed champion and another undisputed champion? For now, Charlo is set for his toughest fight yet when he moves up two divisions to fight another undisputed champion in super middleweight king Canelo Alvarez on Sept. 30 in Las Vegas. Barring a major upset, Alvarez should win that fight and going by Charlo's comments, don't expect him to stay at 168 — he plans on returning to his division.

So why not book Charlo vs. Crawford afterwards? The pair have already been going at each other in the past with Crawford also previously stating his interest in moving up. He's already unified two divisions — imagine if he was able to become unified champion in a third along with being a four-division champion overall? Crawford's claim to the top of the pound-for-pound rankings would be virtually uncontested. Heck, Crawford was even building a fight up with Charlo during his contest with Spence as during a knockdown, “Bud” made a gesture with his crotch towards an in-attendance Charlo and said he was next.

The timeline would also match up as Charlo is facing Alvarez just over two months on from Crawford's win over Spence. More than anything, it'll be another chance to see just how good Crawford really is as he takes on a bigger man in Charlo.

Jaron Ennis

When it comes to the welterweight division alone, this is by far the most intriguing option for Crawford. Jaron Ennis is the current IBF interim welterweight champion with a 31-0 record with 28 wins coming by way of knockout. He's a physical threat who possesses speed, power and skill. Most of all, he's flashy and entertaining, having received props and support from Crawford even during his amateur days.

All that aside, he's 26 — nine years the junior of Crawford — and certainly approaching his prime if he's not in it already. The only knock on him is that he is yet to face a true elite welterweight just yet. But when you're as good as “Boots” is, why not go straight for the king? Crawford would still be the favorite, as he would against any other 147-pounder in all likelihood, but Ennis would certainly represent the biggest threat to him in the welterweight division as things stand. The Philly native is certainly confident in his chances as well after Crawford stated he'd be a dead body if they fought.

“He a walking victim,” Ennis texted popular podcaster Wallo. “Stay at 47 so we can get active.”

Keith Thurman

Another option in the welterweight division is a big name that Crawford is yet to fight in former WBA and WBC 147-pound champion Keith Thurman. Injuries have taken its toll on Thurman who has only competed three times since early 2017. However, his last outing was an impressive showing against Mario Barrios in a unanimous decision win in February last year.

Following Crawford's win over Spence, Thurman — who was in attendance — called the champion out as he seemingly wants to get the next shot. He also stated he wouldn't be flat-footed like Spence was.

Whether he gets the fight remains to be seen, especially as “One Time” appears more likely to fight former champion Yordenis Ugas next. But should Thurman come out on top in that potential matchup, why not go ahead and book the Crawford fight? It's a fight that seemed destined to happen a few years ago and although his stock has gone down in recent years, it's easy to forget that Thurman looked the most likely to unify the division at one point when he held two belts.

Crawford would still be a massive favorite and would likely win as this is a fight that would have been much closer a few years ago. However, Thurman is a big name that would look good on his resume and would certainly help sell a fight.