But let’s begin with the program’s most newsworthy selection — mezzo-soprano Ashley Dixon’s phenomenal performance of the aria “Dopo notte” from Handel’s opera Ariodante. After two years as an Adler, Dixon is far from an unknown quantity, yet this was the first time she had ever sung anything here from the Baroque repertoire. It turns out she’s a master at it. She’s got a robust instrument full of beguiling vocal colors (OK, that we knew), as well as the formidable technical command to unleash streams of glittering coloratura with precision and panache. From her throaty low register to her commanding high notes, all of it was delivered with equal assurance. This would have been a showstopper under any circumstances, but the fact that Dixon’s Handelian wizardry was such a well-kept secret only added to the jolt. It was like watching an ordinary person walk into a phone booth and emerge with a hitherto unsuspected superpower.