While the US were boosted by the presence of star forward Folarin Balogun, whose one-game red-card suspension was controversially lifted by FIFA, American defenders were at fault in a pair of first-half goals on Monday (Tuesday AEST) and goalkeeper Matt Freese's gaffe gave the Red Devils a third early in the second half.
Second-half substitute Romelu Lukaku added Belgium's final goal in the third minute of added time.
Seeking a first World Cup title, Belgium knocked the Americans out in the round of 16 for the second time in 12 years and extended their unbeaten streak to 18 games. The Red Devils play 2010 champions Spain on Friday in California for a semi-final berth against France or Morocco.
Malik Tillman levelled at 1-1 midway through the first half with his second free kick goal of the tournament, but Mauricio Pochettino's men conceded just 61 seconds after the ensuing kick-off.
After winning three games in a World Cup for the first time in this expanded 48-nation tournament, the Americans failed in their quest to reach the quarters for the first time since 2002 and lost to Belgium for the seventh-straight time since a victory at the initial tournament in 1930. The US have dropped 11 of their last 12 games against European opponents, winning only their round-of-32 match against Bosnia-Herzegovina.
De Ketelaere put Belgium ahead in the eighth minute, the first time in this year's World Cup the US conceded first.
Tillman's goal in the 31st energised a largely red-white-and-blue crowd of 66,925 in Seattle, but De Ketelaere damped that and assisted on Hans Vanaken's 57th-minute goal after Freese lost control of the ball in front of his net.
All six CONCACAF and Asian nations have now been eliminated, with the co-hosts US, Mexico and Canada all falling in the round of 16. All quarter-finalists will all come from Europe, South America and Africa.
Belgium pressed from the start and Dodi Lukebakio's diagonal pass led to the opening goal. Leandro Troussard's cross found its way into the penalty area, where De Ketelaere redirected the ball into an open net.
Tillman's free kick deflected off Vanaken's head and to the left of goalkeeper Thibaut Courtois, who had dived right.
De Ketelaere outjumped Tim Ream and headed past Freese in the 33rd minute for his eighth international goal and Belgium built a two-goal lead when Freese was tackled and Vanaken's first-time shot from 35 yards deflected in off Ream, who tried for an off-balance clearance.
Lukaku entered in the 67th minute and scored after Belgium stripped the ball from defender Chris Richards.
