Billie Eilish looks retro chic in vintage Michael Jordan jersey for headline gig at Lollapalooza music festival in Chicago

Lollapalooza kicked off its annual music festival in Chicago's Grant Park with Billie Eilish getting in the spirit of the Windy City.

The Ocean Eyes singer, 21, wore a vintage Michael Jordan #23 Chicago Bills jersey as she performed her night one closing set at the four-day festival. 

The Bad Guy hitmaker's hair was dyed black and worn in high pigtails. 

The Los Angeles native paired the jersey with a long-sleeved t-shirt under it, long, baggy basketball shorts and athletic shoes with black socks. 

She kicked off her 24-song setlist with Bury a Friend and debuted the first live performance of her song from the Barbie soundtrack, What Was I Made For - which is one of the three songs off the Barbie soundtrack in the top five. 

Country singer Lainey Wilson, 31, also rocked the audience on the first day of the festival with a short and sweet 11 song setlist.

The Yellowstone actress looked pretty in a bohemian-style outfit consisting of a long-sleeved, cropped, ruched cream-colored top and grey bell-bottom pants.

The Watermelon Moonshine singer finished her look off with a wide brimmed black hat and rose-colored sunglasses. 

Karol G, 32, also played a  20 song set on the opening night of the festival and she brought her energetic Latina spirit to Grant Park.

The Colombian singer wore a white, fringed, tongue and lip logo halter top reminiscent of the Rolling Stones' Hot Lips logo with a pair of tiger striped pants.

Her waist length, pink hair flowed down her torso in loose waves.  

Carly Rae Jepsen, 37, looked angelic and joyful in a light blue chiffon look featuring a mini dress and cape which she paired with matching light blue, lace-up booties.

Her long blonde hair and blunt-cut bangs were styled straight as she pranced around the stage.

The Call Me Maybe singer performed a 25 song setlist that included two encores. 

Lollapalooza was created in 1991 by Jane's Addiction singer Perry Ferrell. It started as a touring festival but several years in it made Chicago its permanent home.

Other acts performing on day one of the event included Portugal the Man, Diplo, Sofi Tukker, Joy Oladokun, Noah Kahan, Men I Trust and Lovejoy.

Kendrick Lamar and The 1975 headline night two on Friday while Odesza headlines  Saturday with featured performances from Maggie Rogers, Yung Gravy, The Revivalists, Morgan Wade, Sylvan Esso and Suki Waterhouse.

The festival closes out on Sunday with performances from the Red Hot Chili Peppers and Lana Del Rey as well as Mt. Joy, the Backseat Lovers, Afrojack, Lil Yachty and Alvvays.