Thirty Seconds to Mars performing on weekend 1 of Austin City Limits, by Dan DeSlover

As Austin City Limits Music Festival marched into the second day of its first weekend, day 2 was definitely highlighted by music icons—and perhaps future ones.

With headliners and top acts such as Foo Fighters and Shania Twain as well as a mind-blowing performance from Alanis Morissette on the American Express stage and a glorious show from the one and only Tanya Tucker, it was heaven for music lovers who appreciate those whose catalog runs deep, including some who haven't played ACL before or in a long time.

The day was further underscored by cameos from tennis legend Venus Williams, who has been on-site all weekend reportedly filming a docuseries for Hulu, one of the main sponsors of Austin City Limits this year. And timed perfectly with the Texas vs. Oklahoma Red River Rivalry game on Saturday, hometown favorite Matthew McConaughey was side-stage over on the Honda stage to show support for his friend and past collaborator Jared Leto as he and his band Thirty Seconds to Mars took over and Leto literally flew in over the crowd before leaping into the sea of fans to greet them and perform as they excitedly sang back his lyrics to him.

It was great vibes all across Zilker Park on Saturday as popular acts such as Jessie Ware, Gus Dapperton and Declan McKenna played in the early afternoon, with buzzworthy favorites such as Arya bringing the heat on a rather mild day weather wise (for Austin). It just so happened that Venus Williams trekked over to the T-Mobile stage for Arya's performance, so that kind of seal of approval was certainly a signal of the newcomer's talents.

Jessie Ware made a dramatic entrance over at Honda, with a sea of excited fans cheering as she made her debut on the stage, dressed in shiny silver ensemble and surrounded by a foursome of dancers.

Coi Leray over at the IHG stage also proved her own recent rise isn't one to be ignored, as she attracted a thick crowd across the park, while asserting her position in a very business music industry, reminding the crowd of her numerous hit singles and her placement at No. 9 on the Billboard Hot 100 charts with her recent track "Players."

On a day which seemed to revel in the aura of its legacy acts later in the day and the evening, it was artists like Leray and later Noah Kahan who reminded the Texas crowd there were very likely future "icons" in the mix amongst the hitmakers like Foo Fighters and Shania Twain.

Noah Kahan greeted the crowd after pausing to note how awestruck he was by the size of the enormous audience surrounding the T-Mobile stage, saying it was "crazy" to think about that many people gathering to watch him. 

"We used to put tickets up for sale in Texas and we'd have to cancel the shows because no one bought them," Kahan told the crowd before he launched into the debut performance of his new Kacey Musgraves collaboration "She Calls Me Back," sans Musgraves on stage, of course.

Over on the American Express stage, Alanis Morissette was hardly just warming up the stage for the Foo Fighters. The Canadian-American star, who released her new album The Storm Before the Calm last year, delighted an extraordinary crowd of fans with rowdy renditions of hit after hit after hit, proving why she remains such a music industry icon after so many years, giving a dynamic performance worthy of a headlining slot.

The night closed with dueling closers Shania Twain and Foo Fighters, the former of which has been in the middle of a triumphant comeback, opening with new material before launching into favorites like "You're Still the One," "Any Man of Mine" and "Man! I Feel Like a Woman!," turning the ground in front of the Honda stage into an all-out honky tonk dance floor.

Foo Fighters, who have also been making their way across the globe and the music festival landscape following their first new album since drummer Taylor Hawkins' death last year, were certainly the big draw of the night, and it was truly a bittersweet moment welcoming Dave Grohl and company back to Zilker Park. To top it off, literally moments after Shania Twain closed out her set on Honda, she popped up at AmEx for a surprise guest appearance with Foo Fighters to play "Best of You."

All in all, it was a great day for music at Austin City Limits.