Mixed Blood Theatre picked two of the company's longtime favorites to star in "Next to Normal," the musical by composer Tom Kitt and lyricist Brian Yorkey that opened Friday at its playhouse in Minneapolis.

Disappointingly, neither Aditi Brennan Kapil, who plays inconsolable mentally ill mother Diana, nor Thomas Jones II, who depicts her husband, Dan, is well-suited to their pivotal parts. These two strong, in-the-moment actors are not able to credibly deliver the songs at the heart of this show.

Thomas' and Kapil's voices frayed off-key when they tried to belt at Friday's opening performance, helping to make this "Normal" a mostly lackluster affair, despite an infusion of first-act humor by director Jack Reuler.

The 2010 Pulitzer Prize-winning musical, which kicks off a disabilities-themed festival at Mixed Blood, would have been a tall order for the company anyway. Alice Ripley, the Broadway star of "Normal" who won a Tony for her indelible turn as Diana, reprised her performance on a national tour that came to the Ordway in May 2011.

That production used a vertical, scaffold-dominated set that made it easy to create the intimate rooms and realms of "Normal." In the tight, converted firehouse space that is Mixed Blood, set designer Joseph Stanley created a striking horizontal playing area, well-lit by Karin Olson, with modular, multifunction props that are adjusted by the actors.

It is mostly well-used by director Reuler, save for the occasional attention-splitting, whiplash-inducing scenes that veer from one end of the set to the next. The musical backing is provided by a swinging sextet led by pianist Jason Hanson.

I was looking forward to seeing Kapil and Jones, both of whom are also capable writers and directors, add singing to their talent list. To their credit, they both sounded soulful when they were not trying to reach their upper register, especially during the musical numbers in which they were joined by Brittany Bradford as daughter Natalie and Ricardo Vazquez as the spirit of their son Gabe.

Bradford and Vazquez are part of a strong supporting cast. She's a beautiful, moving singer with lovely phrasing. And she leavens her highly sarcastic and potentially tiresome role with charismatic sweetness. Vazquez is a heartthrob-in-the-making who brings a vivacious spirit and affecting emotionality to his disembodied character.

The biggest "Normal" supporting cast member is Regina Marie Williams, who was still potent, despite vocal problems, as a rock-star psychiatrist who literally is a rock star. Williams makes this role, depicted by a man on Broadway, her own, delivering powerfully with wit and verve in a production that could use sharper star turns.

Rohan Preston • 612-673-4390