A 'frustrated' Simon Cowell warns 'AGT' semifinalists to 'get better.' Here's who advanced.

The final spots in the semifinals are up for grabs on "America's Got Talent."

But if you ask Simon Cowell, out of all 12 acts that performed Tuesday, "only three (contestants) were better than their first audition." 

"When you come on this stage, you got to bring your 'A’ game," Cowell said, warning all competitors during Wednesday's results show. "You got to get better if you want to win… I was frustrated not for myself, but for the acts."

Good thing it's up to America to decide who moves on to the semifinals. Only seven will advance, while the million-dollar dream for five of the acts will end tonight. 

Season 13 "AGT" and "America's Got Talent: The Champions" winner Shin Lim returned Wednesday to perform a magical duet with violinist Lindsey Stirling, a quarter-finalist from Season 5.

Last night on 'AGT':Wild card winner Storm Large returns to competition, but fails to impress Simon Cowell

Here's what happened during the "America's Got Talent" live results show:

The fans' picks

The five acts that received the most votes automatically advanced.

Rialcris was the first act to move forward following their death-defying acrobatic routine. Sofía Vergara, who has a soft spot for fellow Colombians, called the trio "perfecto… Don’t change a thing."

Quick change artist Léa Kyle, Heidi Klum's Golden Buzzer winner, was also safe. Klum said, "You made your Golden Buzzer mama really proud."

ChapKidz joined them in the safe zone soon after, following their "sensational" dance routine that Cowell dubbed the "best act by a mile" last night. Mandel went a step further Wednesday, calling them "the best dancing act we’ve had on Season 16."

World Taekwondo Demonstration Team, Terry Crews' Golden Buzzer act, and singer Brooke Simpson both advanced in a dramatic reveal that made viewers believe only one was moving forward. "I’m not surprised with what just happened," Vergara said. 

The face-off

Michael Winslow (voicetramentalist), Storm Large (singer) and UniCircle Flow (unicycle group) finished in the middle of the pack and were on the brink of elimination.

"I'm really sad to see you guys in their position," Heidi Klum said. "This competition is tough this time around."

The three acts went head-to-head in a live-voting round for the "Dunkin' Save," where fans had the opportunity to rescue only one performer. Whoever received the most votes in a 30-minute flash round would move on.   

In the end, viewers saved Winslow. He let his sounds do the talking and produced a palpitating heart sound to explain just how nervous he felt.

But the final results weren't in just yet. The judges had a chance to save either UniCircle Flow or Large, the first-ever winner of "AGT: America’s Wildcard." 

“It’s so hard because I believe in both of you… but if I don’t pick one they are going to fire me,” Vergara said, before picking UniCircle Flow. Klum voted for Large. Cowell called the choice "tricky," but selected UniCircle Flow. Mandel agreed, sending UniCircle Flow into the semifinals.

The act with the most overnight viewer votes would advance: UniCircle Flow.

Eliminated

The four acts with the fewest votes – Klek Entos (magician); ANICA (singer); Keith Apicary (dancer); and The Curtis Family C-Notes (band) – were eliminated.

Large was also sent packing. 

Next week

"America's Got Talent" will return Tuesday for the first semifinal round (NBC, 8 EDT/PDT), where 12 other acts will try to blow America away to advance to the finals.

Next week’s performers include Dustin Tavella (magician); Michael Winslow (voicetramentalist); Korean Soul (vocal quartet); Tory Vagasy (singer); Gina Brillon (comedian); Peter Rosalita (singer);  Aidan Bryant (aerialist); Madilyn Bailey (singer); UniCircle Flow (unicycle dance group); and Golden Buzzer winners Jimmie Herrod (singer) and World Taekwondo Demonstration Team (martial arts group).