The two sides arrived in the Playoffs with almost identical form - both were on four-match winning runs and had only suffered one loss across seven matches each in the Group Stage.
But that didn't stop the Americans drawing first blood inside the first five minutes; after Juuso Parssinen got called for hooking, the USA took only 23 seconds to take advantage of the powerplay, as a nice pass from the left from Logan Cooley picked out Conor Garland, who fired home.
It took Finland eight minutes to draw level with a powerplay of their own following a delay of game penalty against Cooley.
Teuvo Teravainen's shot from the left ricocheted away off his own teammate Juho Lammikko but fell kindly for Eeli Tolvanen to sweep in his seventh goal of the tournament.
Finland took the momentum into the second period and thought they had used it to full effect two minutes in when Mikael Pyyhtia found the net, only for the goal to be disallowed following a challenge.
But five minutes later, a holding call against Team USA's Frank Nazar allowed the Leijonat to take the lead.
Patrik Puistola miscontrolled the puck the first time his teammates set him up to shoot, but after recycling well, Teravainen looked for the Orebro forward again and this time he buried his shot past Jeremy Swayman.
However, the US responded well to going behind and were level again with just over five minutes left in the second, as Zeev Buium found Matthew Beniers on the right, his shot was saved by Juuse Saros but Buium followed in scored on the rebound.
Puistola was called for tripping in the same play, and that allowed the USA to retake the lead soon after on another powerplay - Garland received a pass from Tage Thompson and tried to force his way in front of the net, before the puck deflected off a defender's stick and looped over Saros.
After 40 minutes, Finland found themselves behind having conceded three goals for just the second time at this World Championship.
Unfortunately for Antti Penanen's side, the defensive setup they prided themselves on deserted them further in the third period, when the Americans opened up a two-goal lead for the first time.
Six minutes after the restart, the United States broke out of their own zone, before Cutter Gauthier and William Smith combined expertly set up Shane Pinto for his first of the World Championship.
Finland went for broke late on, pulling Saros in favour of an extra attacker, but it backfired and Clayton Keller found the empty net to make the final score 5-2.
It's disappointment for the Leijonat who harboured ambitions of getting back on the podium, but it's the USA who move onto the Semi-finals.
Joining them in the last four are Switzerland, who made light work of their Quarter-final, brushing Austria aside, 6-0.