After three physically and mentally grueling matches in group play, the United States escaped to the Round of 16 to meet Belgium on Tuesday at Arena Fonte Nova in Salvador, Brazil.

Making a team record second-straight trip to the knockout stage, the U.S. can take away several positives from the first two weeks of the World Cup. Goalkeeper Tim Howard has been sensational, forward Clint Dempsey hasn’t missed a step in the attack in spite of running mate Jozy Altidore’s absence due to a hamstring injury, and midfielder Jermaine Jones has knocked down opposing backlines to embrace his role as the Yanks bruiser.

There were, however, plenty of negatives for head coach Jurgen Klinnsman to pick apart. The 2-1 victory over Ghana was truly miraculous, considering how the U.S. midfield struggled against the more athletic Black Stars and could barely maintain possession.

The Portugal draw could have been a victory if not for Cristiano Ronaldo, but with fatigue setting in, the U.S. defense lost their mental focus and allowed Varela to convert Ronaldo’s perfect cross.

Against Germany, the midfield was again exposed. The Yanks generated one shot on goal and lost the possession battle by a wide margin, 63-37. Howard was again in top form, adding five saves and upping his total during this Cup to 13.

In the knockout stage, the U.S. can ill afford to leave the Everton star so exposed -- especially against a Belgium squad that won all three group-stage matches. This talent-rich Red Devils have one of the best attacks of the remaining 16 nations, and could make life miserable for the U.S. if they fully realize their potential.

Here are several players to keep an eye on throughout the elimination match.

Michael Bradley, M, USA

It was Bradley’s giveaway which led to Portugal’s final goal and cost the U.S. a second victory, and the play was somewhat indicative of the decorated 26-year-old’s World Cup thus far. He has struggled in all three matches, and his performance against Belgium will likely be heavily scrutinized.

Bradley is typically the most consistent, and perhaps the most versatile, player on the U.S. squad. He can facilitate the attack and drop back to help out the defense. Thus far, his passes haven't been crisp, and he has failed to effectively maintain possession.

Bradley’s best game could emerge against the Belgians with midfielder Steven Defour, owner of 43 senior caps, suspended for the match after picking up a straight red in the final group match against South Korea. Belgium’s Mousa Dembele and Axel Witsel will also enter the match with yellow cards, and their defense could suffer for fear of a second booking.

Vincent Kompany, D, Belgium

One of the highest rated defenders in the world, the 28-year-old Manchester City star played through a groin injury in the first two group matches before sitting out against South Korea. He reportedly re-aggravated the knock during training Wednesday, but with nearly a week off to rest for the match, Kompany could be near 100 percent come kick-off time.

Powerfully built, but blessed with quick feet and skills, Kompany is the type of back line leader the U.S. feared after Altidore went down. Kompany’s capable of knocking down even the strongest of strikers.

Klinsmann may still insist his strikers go right at Kompany to test his fitness, and perhaps expose the Red Devils lack of depth in the backline. Belgium only has three other defenders to back up Kompany, and one of them, Thomas Vermaelen, is also battling a hamstring injury.

Geoff Cameron/Omar Gonzalez, D, USA

Cameron’s failed clearance led to Nani’s goal in the Portugal match, and he continued to struggle against Portugal’s much quicker attackers. That led to Gonzalez’s start against Germany, and the 25-year-old showed just one sign of nerves, but two important stops inside the penalty area denied the Germans a convincing victory.

Gonzalez did pick up a booking against Germany, which could translate into a start and redemption for Cameron.

If any player can get past his early troubles its Cameron. He made the jump from Major League Soccer to English Premier League in 2012 and last season helped Stoke City field one of the better defenses in the league.

Klinsmann could sub in Gonzalez later in the match, especially if the U.S. has the lead. Though Klinsmann takes big risks, the Yanks need a defender willing to put himself on the line in a big situation.

Romy Lukaku, F, Belgium

Lukaku and Eden Hazard were supposed be a punishing and dynamic attack duo, but other than defender Jan Vertonghen’s goal in the win over Russia, every Belgian goal has come from the bench.

Lukaku, 21, was expected to build on his stellar 15-goal loan-spell with Everton and carry the Belgian attack. But in two matches (he sat out against South Korea) Lukaku’s squeezed off one shot. It will be interesting to see if he steps up against the U.S.

Clint Dempsey, F, USA

Klinsmann said on Friday that he’s “optimistic” Altidore will make his return against Belgium. An excellent sign for the U.S., but it does little to relieve the pressure or change Dempsey’s role.

The 31-year-old has a way of making plays out of nowhere, and at the best possible time. Dempsey’s goal against Ghana will go down in history as the fifth-fastest scored in a World Cup, and after bodying his second goal into the net, the U.S. held a 2-1 lead over Portugal in the 81st minute and a win seemed all but locked up.

Altidore’s presence might mean less Belgian defensive pressure aimed at Dempsey, but the U.S.’s quarterfinal hopes may begin and end at the feet of the Texas native.