Bryant drilled four three-pointers in succession to chants of "Kobe, Kobe" from the North Greenwich Arena crowd as the Americans ran away from a fatigued Australian team that had given their all for 30 rousing minutes.
"Kobe's been usually the best player every night we play (in the NBA) so it's great to see him go off like that," US point guard Chris Paul said about the Los Angeles Lakers leader who enjoyed his biggest game so far in this Olympics.
"He could do that every night but our team is so deep he doesn't need to."
The victory completed the line-up for Friday's medals round games, where the winners advance to the gold medal match, while the losers contest the bronze on Sunday's closing day of the London Olympics.
Defending champions United States will play Argentina, while Spain, losing finalists to the US in Beijing, take on Russia.
Bryant led the winners with 20 points in just under 20 minutes on the court, while LeBron James registered a triple double with 11 points, 14 rebounds and 12 assists.
Patrick Mills paced Australia with 26 points, with Joe Ingles adding 19.
The Australians kept in touch with the Americans into the third quarter when, after an 11-0 run to start the period, they drew within 56-53. They were still a respectable 84-70 behind heading to the fourth.
"You're going to think I'm crazy but we really thought we could win that game," said Ingles.
"We know who they are, we know what they can do but they are human, they do make mistakes. No one shoots 100 per cent. We got it back to three at the start of the second half but then we made some mistakes and that team will just punish you."
Bryant's scintillating shooting display ignited a 16-2 run that turned the rest of the game into a US highlights reel.
"We got off to a horrible start in the second half. They were playing well in the first half and then we got that bad start and then they played great," said US coach Mike Krzyzewski.
"The offensive rebounding was a key factor. LeBron made a couple of offensive rebounds and then Kobe made a couple of big defensive plays that went to the offensive end, and we kind of exploded from there."
Six US players scored double figures, including Deron Williams with 18 points, Carmelo Anthony (14) and Kevin Durant (14).
The Americans are familiar with Argentina, who trailed by only one point at halftime in their preliminary round game before the US team exploded for 42 points in the third quarter for a runaway win.
They also played a competitive game against the US in a warm-up in Barcelona before coming to London.
"They're better together than they are individually. They make each other better and they have the heart of a champion," Krzyzewski said about an Argentine team led by Manu Ginobili and Luis Scola that won Olympic gold in 2004 and bronze in Beijing.
"We had two tough games against them and I expect we'll have another."
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