St. Louis City look to extend their perfect start to the Major League Soccer season on Saturday as a depleted Atlanta United bid to preserve their unbeaten record despite missing several players on international duty.

Expansion side St. Louis have emerged as the early feel-good story in MLS this season, with a 100% record after four straight victories in what is the club's debut campaign.

Former South Africa international Bradley Carnell has forged a tight-knit squad made up largely of players who struggled to establish themselves elsewhere, and Carnell believes that has left his team with a point to prove.

That fierce determination to confound pre-season scepticism about City's chances in the league has carried Carnell's men to impressive away wins over Austin F.C. and Portland Timbers as well home victories over Charlotte and San Jose last weekend.

It is the best start to a campaign ever made by an expansion club, and Carnell is confident St. Louis can keep the run going as they travel to Utah to face Real Salt Lake on Saturday.

"The boys were confident from day one," Carnell said of his team's blistering start to the season. 

"The boys were angry from day one that no one believed in them. So yeah, we've got the chip on the shoulder. 

"But now we've shown that it's not just about having a chip on the shoulder. We can compete, we can dominate, we can take control and we can execute."

One advantage of St. Louis' recruitment strategy is that they will face minimal disruption from this week's international window. 

Only two players who featured against San Jose on Saturday will be missing this weekend –- Canadian defender Kyle Hiebert and US under-19 international Miguel Perez.

The same can not be said for St. Louis' pace-setting counterparts in the Eastern Conference, Atlanta United.

Atlanta remain unbeaten with three wins in four games, including a rampant 5-1 mauling of Portland at home last weekend. 

But they will be missing no fewer than seven first-team players for Saturday's trip to the Columbus Crew, most notably Argentine World Cup-winner Thiago Almada.

The 21-year-old Almada has taken MLS by storm this season with four goals in four games, but is absent on international duty for Argentina's friendlies against Panama and Curacao.

Atlanta are one of several teams who will be forced to juggle resources this weekend.

Minnesota United, Orlando City and Philadelphia Union also have seven players on international duty.

Los Angeles FC, second in the Western Conference behind St.Louis, will have four international absentees when they host Dallas at BMO Stadium.

Third-placed Seattle, meanwhile, have six international players missing for their trip to Sporting Kansas City. 

Canada's CONCACAF Nations League game against Curacao on Saturday also causes a headache for Toronto FC head coach Bob Bradley.

Toronto will be missing four Canadian internationals -- Ayo Akinola, Mark Anthony-Kaye, Richie Laryea and Jonathan Osorio -- as well as El Salvador goalkeeper Tomas Romero for the team's away fixture with San Jose.