Nick Jonas and Demi Lovato at Sleep Train

Demi Lovato performs at the Sleep Train Amphitheater in Chula Vista.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

A woman holds a child as they watch Nick Jonas perform.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Nick Jonas performs at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Fans sway their arms as they watch Nick Jonas perform.  (Hayne Palmour IV / San Diego Union-Tribune)

Demi Lovato performs at the Sleep Train Amphitheater in Chula Vista.  (Hayne Palmour IV / San Diego Union-Tribune)

Demi Lovato performs at the Sleep Train Amphitheater in Chula Vista.  (Hayne Palmour IV / San Diego Union-Tribune)

Demi Lovato performs at the Sleep Train Amphitheater in Chula Vista.  (Hayne Palmour IV / San Diego Union-Tribune)

Fans sing along as Demi Lovato performs.  (Hayne Palmour IV / San Diego Union-Tribune)

A fan sings along as Demi Lovato performs.  (Hayne Palmour IV / San Diego Union-Tribune)

Demi Lovato performs at the Sleep Train Amphitheater in Chula Vista.  (Hayne Palmour IV / San Diego Union-Tribune)

Demi Lovato performs at the Sleep Train Amphitheater in Chula Vista.  (Hayne Palmour IV / San Diego Union-Tribune)

Demi Lovato performs at the Sleep Train Amphitheater in Chula Vista.  (Hayne Palmour IV / San Diego Union-Tribune)

Mike Posner performs before Nick Jonas and Demi Lovato.  (Hayne Palmour IV / San Diego Union-Tribune)

Mike Posner performs before Nick Jonas and Demi Lovato.  (Hayne Palmour IV / San Diego Union-Tribune)

Chord Overstreet performs before Nick Jonas and Demi Lovato at the Sleep Train Amphitheater.  (Hayne Palmour IV / San Diego Union-Tribune)

Fans use their phones to record Chord Overstreet performing before Nick Jonas and Demi Lovato.  (Hayne Palmour IV / San Diego Union-Tribune)