A little over a year ago, Kendrick Lamar had a comfortable perch as one of hip-hop’s most popular performers, and also the most pious. Then came his monthslong quarrel with Drake, which turned into a referendum on ethics in hip-hop (and life). That led to the emergence of Lamar as a maker of tsk-tsking anthems, which turned into his leanest and meanest album to date. Then came a valedictory performance at one of the biggest stages in the world: the Super Bowl halftime show in February.

The outlier song on that album, “GNX,” is the SZA duet “Luther,” which has reigned atop the Billboard Hot 100 for 11 weeks. It’s both sweet and dour, a love song that somehow romanticizes the obstacles that get in the way as much as the affection itself.

Despite the success of “Luther,” Lamar and SZA aren’t necessarily natural duet partners; they’re two complementary but not overlapping styles of sentimentalist. Lamar treats remembrance as if it’s a moral act, and SZA expresses a kind of agitation about looking backward. They’ve shared a record label and collaborated several times over the past decade — some good songs, some great ones, all of them in slight tug of war with themselves.

That added a layer of complexity to their current outing, the Grand National Tour, which came to MetLife Stadium in East Rutherford, N.J., on Thursday night for the first of two performances. Even if the overall song count tilted a bit in Lamar’s favor, it was in essence a co-headlining event: Lamar, his popularity at its peak, touring stadiums for the first time, while SZA takes a victory lap for “S.O.S.,” her beloved 2022 album.

Lamar’s set list right-sized the role of the Drake beef in his career arc — important and perspective shifting, but not dominant. Credit…Graham Dickie/The New York Times

For almost three hours, Lamar and SZA traded control of the stage, a few songs at a time, a conceit that gave the performance quickness and unpredictability. Sometimes they’d hand off the spotlight with a tender duet, little dollops of warmth amid the high-energy, boldly produced presentation. (Others have taken this trade-off approach before: Beyoncé and Jay-Z, Charli XCX and Troye Sivan.)