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It had been so long since Megadeth played in San Antonio, fans had to wonder if they were ever going to see the Big 4 thrash band in the Alamo City again.

Ever since that Sept. 25, 2010, gig inside the AT&T Center, the venue's regular inhabitants, the Spurs, had won an NBA championship -- three seasons ago. Megadeth also had not only played its own Gigantour in Corpus Christi as well as shows in Austin every so often, but vocalist/guitarist and band founder Dave Mustaine even took the time to move to the Live Music Capital.

Sunday proved to be more than worth the wait.

Playing on the main stage outside the AT&T Center, Megadeth brought back its dizzying riffs, pounding drums and bass and brand of thrash old and new to the fourth annual River City Rockfest before the extravaganza's largest official crowd of "more than 27,800." One day after new guitarist Kiko Loureiro held an instructional clinic at Sam Ash Music Store and original bandmates Mustaine and bassist David Ellefson signed autographs at FYE inside Ingram Park Mall, Megadeth delighted and excited the metal masses and casual followers on a hot and humid 12-hour day.

Armed with Soilwork drummer Dirk Verbeuren, filling in for Chris Adler who has commitments with Lamb Of God through late June, Megadeth opened with the familiar punishing sounds of 1990 classic "Hangar 18." Mustaine and Co. then gave their first taste of latest CD Dystopia, which dropped Jan. 22, with the album's opening track "The Threat is Real" before Mustaine declared song No. 3 to be "about the weather" as the band rocked into "Sweating Bullets" (see setlist in slideshow).

The mix of old and new continued with "Fatal Illusion" and "Symphony of Destruction" (watch AXS' footage of both here), before Megadeth signed off with its traditional "Peace Sells (But Who's Buying?)" and "Holy Wars (The Punishment Due)."

Playing the final show of its U.S. tour, Megadeth was slated to depart for Italy 24 hours later on Memorial Day before Mustaine could return to his Austin home. Perhaps mindful of that, Loureiro soaked in the festival as a fan three hours earlier by standing at the side of the stage to catch Sixx A.M.'s set.

Despite the fact the Rockfest was being headlined by Disturbed -- which is fronted by Mustaine's fellow Austin resident and friend David Draiman, who collaborated on Megadeth's 2013 CD Super Collider on "Dance in the Rain" -- there were no extra jam sessions during the set. Just classic and new thrash material, Megadeth style. Megadeth had officially come to the River City Rockfest. It saw, thrashed and conquered.

Will it take another six years before Megadeth returns? The threat of such a musical calamity remains real. But just as possible is that Megadeth could headline its own tour package later this year, if not in San Antonio then most certainly Mustaine's current hometown up Interstate 35.

For now, 27,000-plus heard Mustaine declare, "You've been great, we've been Megadeth" at a pulverizing performance 5 1/2-plus years in the making. With the group going as strong as ever, it shouldn't take as long before those words, and particularly those unique riffs, will be uttered and played again in S.A.

To watch AXS' exclusive River City Rockfest interview with Hatebreed, click here. Stay tuned for plenty more coverage of the festival's bands including Disturbed, Scorpions, Sevendust, Bullet For My Valentine, Hellyeah, DevilDriver and more.