World Cup Tuesday best bets: Spain to best Morocco

The round of 16 concludes on Tuesday with games featuring perennial contenders against a couple of scrappy dark horses.

Let's take a closer look at the best way to attack those matches with a pair of best bets.

Morocco (+500) vs. Spain (-170)

Morocco opened a lot of eyes in the group stage, claiming top spot in a difficult group that most people didn't expect the Moroccans to get out of at all.

While battle-tested, the Atlas Lions haven't come up against a side of Spain's caliber. The Spaniards only won one of three games but netted nine goals, posted a plus-6 differential, and registered strong underlying metrics. Their expected goal differential of plus-2.5 is among the best in the tournament.

Morocco has some talented players - and a strong backline - but it can't match this Spain team in terms of raw ability.

Spain has more dynamic ability on the ball, and its clinical team passing figures to be too much to overcome - especially with in-form attackers like Ferran Torres and Alvaro Morata on the receiving end of all those chances.

I expect Spain to prevail inside 90 minutes, but I like the idea of throwing an under of 3.5 goals into the mix to provide more value.

Both sides are strong defensively, with Spain (2.7 xGA) and Morocco (2.8 xGA) allowing less than one expected goal per fixture.

Morocco's game plan will undoubtedly be focused on slowing the game's pace and disrupting Spain's precision passing and remarkable build-up play. The Spaniards, meanwhile, will no doubt be happy to dominate the ball and pass it around as long as it takes to create the opening they're looking for.

Spain should dominate possession, but this Morocco side is formidable defensively. It won't just fold and make life easy for Spain.

While Spain should prevail, it'll be a grind-it-out affair rather than one where the two sides trade chances in open play.

Bet: Spain and Under 3.5 (+110)

Portugal (-110) vs. Switzerland (+320)

I wasn't overly high on Switzerland heading into the World Cup. Its play in the lead-up wasn't inspiring, and the side doesn't possess much dynamic talent.

The Swiss have really impressed me through three games, though. They won two of three matches and posted a solid plus-1.4 expected goal differential.

What really stood out to me was La Nati's ability to create opportunities consistently. I had concerns they'd be able to pull defenses apart and generate quality looks on goal, but they have done just that. Switzerland piled up 4.4 expected goals in the group stage, a total bested by only eight countries.

Switzerland just might have the chops needed to cause Portugal real problems. The Portuguese looked vulnerable without the ball in the group stage, allowing 3.9 expected goals and four actual goals over three games.

For perspective, Australia, Poland, and Japan were the only teams that conceded more expected goals and advanced beyond the group stage. The first two were bounced immediately in the knockout round, and Japan will likely follow suit.

I think Switzerland is going to hang around in this game and give Portugal a difficult fixture.

Bet: Switzerland +0.5 (-115)

Todd Cordell is a sports betting writer at theScore. Be sure to follow him on Twitter @ToddCordell.