The US made the most of Serbia's absence to clinch their sixth Hopman Cup title with a 2-1 win over Belgium in Perth on Saturday.
America's pairing of John Isner and Bethanie Mattek-Sands beat Justine Henin and Ruben Bemelmans 6-1 6-3 in the deciding mixed doubles to secure the title, after the singles rubbers were split at 1-1.
Isner had earlier defeated world No.178 Bemelmans 6-3 6-4 in 58 minutes following Henin's hard-fought 7-6 (8-6) 6-3 win over Mattek-Sands.
But it could have been a different story had former world No.1 Ana Ivanovic not been struck down by a stomach tear.
Serbia's powerful pairing of world No.3 Novak Djokovic and Ivanovic had qualified for the final after romping through their group stage.
But the top seeds were forced to withdraw following Ivanovic's injury, handing Belgium a place in the final and boosting the title hopes of the unseeded US in the process.
Belgium were completely outclassed in the mixed doubles, losing in 58 minutes as the US secured another piece of Hopman Cup silverware to add to their title wins in 1997, 2003, '04, '06 and '08.
Earlier, Henin saved two set points in the first set and came back from a break down in the second to get Belgium off to a flying start in the women's singles.
Both Henin and Mattek-Sands struggled to hold serve in the opening set, which saw 10 consecutive breaks of serve at one point.
World No.58 Mattek-Sands shot out to a 3-1 lead in the second set but once again Henin came to life, reeling off 18 of the last 19 points of the match to cruise to the win.
Henin, who only found out late on Friday she would be playing in the final, said she struggled to mentally prepare for her singles match.
"I planned not to play tennis yesterday and I was in my room and ... they told me 'you will play the final tomorrow'," Henin said.
"It was strange because mentally I was really focused on leaving for Melbourne on Sunday."
In the men's singles, the powerful serve of world No.19 Isner was too hot to handle for Bemelmans, who put up a good fight but simply didn't have the weapons to get past his higher-ranked opponent.