After beating American Charles Howell III 6&4 in their last-16 clash yesterday morning, Rahm thrashed Denmark’s Soren Kjeldsen 7&5 in the afternoon’s quarter-finals to book his place in the last four.
The 22-year-old, who was the world’s top-ranked amateur while studying at Arizona State University, is currently 25th in the world after winning his first PGA Tour title in the Farmers Insurance Open in January.
And he could rise as high as tenth in the standings with victory in just his second World Golf Championships event, having finished tied third in the WGC-Mexico Championship earlier this month.
Rahm has not trailed at any point in his five matches this week at Austin Country Club and was three up on Kjeldsen after six holes, aided by an eagle from just four feet on the par-five sixth. A par was good enough to win the eighth and birdies on the tenth and 12th helped Rahm seal another emphatic victory in the £7.8million event.
By joining the European Tour on 1 March as an affiliate member for the 2017 season, Rahm is eligible to earn Ryder Cup points when qualifying begins on 31 August.
Commentating on Rahm’s match for Sky Sports, Westwood said: “His game is by no means one-dimensional. He’s got a lot of different shots, even for a young player.
“I think his game is really impressive. He’s definitely a big star of the future.”
Rahm, who will face Bill Haas in this morning’s semi-final after the American beat compatriot Phil Mickelson 2&1, said: “The only thing I could have done better is maybe make that putt on 11 and that’s about it.
“There’s not many rounds of golf where a player looks back and says I cannot play any better and today was one of those.
“Last time I said that was Torrey Pines [scene of his win in the Farmers Insurance Open]. Today it was the exact same way. I did a really good job.”
Rahm was so dominant in his two matches yesterday that he ended them both on the 14th hole. The rookie has yet to play the 18th hole at Austin Country Club.
Mickelson had never trailed in any of his first four matches and led for 54 of the 57 holes he had played, but immediately fell behind in the quarter-finals when Haas birdied the opening hole.
And although Mickelson got back on level terms at the next, Haas won the third, fifth and sixth and responded to Mickelson reducing his deficit on the seventh by making a birdie on the ninth to move three up at the turn.
Mickelson won the tenth and 12th holes to get back to one down, only for the impressive Haas to birdie the 15th and halve the next two holes to seal victory.
American Dustin Johnson will play Hideto Tanihara of Japan in this morning’s other semi-final. Johnson, the world No.1, defeated Sweden’s Alex Noren 3&2 in their quarter-final tie, while Tanihara beat England’s Ross Fisher 4&2.
Fisher’s last-16 4&3 victory over Bubba Watson, though, is expected to take the 36-year-old into the world’s top 50 tomorrow and secure a first appearance in the Masters since 2012.
“Hopefully it will be good enough,” said Fisher afterwards.