Rock singers say it a lot when they're thanking a crowd, but Mike Doughty wasn't just going through the motions when he assessed Saturday's installment of the McNally Smith River Rocks Festival on St. Paul's Harriet Island as "a perfect night."

The second day of the second annual two-day, two-stage event -- a benefit/attention-getter for the city's McNally Smith College of Music -- went off well enough to declare it the best new music fest the Twin Cities has seen in several years.

It had the diversity that Harriet Island's best-known tenant, Taste of Minnesota, sorely lacks. On the other hand, it had Taste's scenic setting, which too many other outdoor concerts in the metro area lack (not that the Basilica Block Party's setup isn't lovely, as parking lots go).

About the only imperfect thing about River Rocks was the relatively lackluster attendance: Only 5,000 or so people showed up both days, a sharp improvement from the first year but still somewhat disappointing considering the golden weather and the fun lineup of familiar if not superstar names.

Friday's show featured a somewhat awkward though admirable mix, with Jakob Dylan's freewheeling country-rock sandwiched between Ozomatli's fiery Latino hip-hop and headliner O.A.R.'s trite jam-band pop.

Saturday's bill, however, flowed cohesively. A local promoter finally put the Twin Cities' best live hip-hop band, Heiruspecs, on stage right before the world's best, the Roots. After that, the show turned into a '90s alt-rock fest, with ex-Soul Coughing singer Doughty, a reunion by local favorites Semisonic and the still-thundering band behind "Lighting Crashes," Live. Throw in the hip mish-mash of younger (and heavily female) local bands on the smaller stage, including Maria Isa, Skirt and Alison Scott, and St. Paul felt pretty dang cool at least for one day.

Semisonic's hourlong set -- only the band's second since it went on semi-hiatus in 2003 -- seemed like the big draw Saturday. It proved to be the musical high point, too.

The trio's feel-good charm feels all the better when you throw in the nostalgia and camaraderie that comes at most reunions. Radio staples like the opener "F.N.T.," the closer "Closing Time" and the in-between highlight "Chemistry" sounded as timeless as most Beatles-inspired pop/rock does -- especially on warm late-summer nights.

The Roots were pretty spectacular Saturday, too. Limited to an hour from its usual two-hour-plus jamathons, the Philadelphia hip-hop stalwarts literally performed nonstop for the first half of their set, tearing through the feisty gems "I Can't Help It" and "In the Music" before breaking into a drum solo. That's right: a hip-hop act with a drum solo. Deal with it.

Saturday's show sporadically harked back to the Take Back Labor Day protest concert on Harriet Island during the Republican National Convention. The Roots' frontman Black Thought urged their young crowd to vote: "You know we have to do better than the last eight years."

Doughty, who performed acoustic with only a cellist at his side, made fun of Sen. Norm Coleman's attack ads on Al Franken: "So, all he has to go on is the guy has said some bad words?"

The only local figure that Wallflowers frontman Dylan mentioned Friday was Twins legend Rod Carew. His spirited, twangy set with a new solo band referenced another ex-Minnesotan musically: His dad. That, too, felt as perfect as most everything else at River Rocks.

See Semisonic's set list at startribune.com/poplife.

Chris Riemenschneider • 612-673-4658