"Taylor Swift is making new friends on her Red tour this summer. Last night in Los Angeles she brought out Tegan and Sara as surprise guests to perform their bouncy, affectionate hit "Closer." As she introduced the sister duo, Swift called their new album, Heartthrob, "one of my favorites of all time. If you've ever had your heart broken, you need to have their album." The Calgary twins arrived midway through Swift's two-hour concert, rising from the Staples Center stage dressed in black and wearing stylish combat boots. Tegan sang first, twisting in place to the heartsick dance hooks: "All I want to know is, can you come a little closer?" Go Backstage With Taylor Swift on Her Huge Summer Stadium Tour The trio worked their way down the catwalk, with Swift in a gleaming white T-shirt reading "Hello Los Angeles." Their voices blended easily on the pop tune. "I notice we have a bouncy crowd," Swift said, encouraging fans to hop along to the message: "Let's make things physical . . . I want you." It was the second of Swift's four sold-out nights at the arena. The multi-platinum host has been inviting guests onstage each night: Cher Lloyd and Sara Bareilles joined her the night before, and on Tuesday she also sang a duet with red-headed opener Ed Sheeran ("Everything Has Changed"). For longtime fans of Tegan and Sara, who began recording as a young indie rock duo with a gift for lovesick melodies, their collaboration with a pop crossover artist like Swift might seem surprising. But Heartthrob showed the singer-songwriters evolving into searing, danceable electro-pop. In recent interviews, both acts have made admiring comments about each other's music. The rest of the night was just as excitable, unfolding a hit parade that sent Swift soaring through the air, strolling down a long catwalk with supermodel swagger and delivering "You Belong With Me" with a quartet of backing singers and dance moves resembling a Sixties girl group. Like Pink and other agile pop contemporaries this year, Swift's concert was musical theatre on an epic scale, down to the color-coordinated sparkly red microphone, ruby slippers and a matching electric guitar. Swift switched to period costume for "Lucky One," wrapped in a snug red Jessica Rabbit gown and trailed by dancers dressed as 1950s newsmen and photographers in fedoras. There were home movies of baby Taylor, following her rise from Nashville teen to Grammy-winning sensation, and songs on the struggles of growing up, including "Mean" and "15." The latter, about her freshman year of high school, was one of several songs that began with Swift alone on guitar or banjo. "I didn't always have 15,000 people waiting to hang out with me on a Tuesday night. It's wild," Swift said to her ocean of fans (dominated by young girls and their parents), who lifted heart-shaped signs and words made of lights spelling out song titles and lyrics. Swift thanked them repeatedly during the night, through multiple costume changes and songs of pure pop and twangy self-determination. The momentum never slowed, even during her many, many remarks on a long line of worthless ex-boyfriends. (You know who you are.)"