If only because of the status of Robert Plant, the concert of the tandem he formed with the bluegrass singer Alison Krauss was one of the most prominent posters of the Festival international de jazz de Montréal. Expectations were high, and the duo more than lived up to it, they were downright amazing.

“We came to bring you sophisticated jazz,” Robert Plant announced, in a mix of French and English after a few songs. The remark was intended to be ironic: the ex-Led Zeppelin singer was amused to have been programmed in a jazz festival. He actually chimed in later that night, saying he wouldn’t call what they’re doing “jazz.” “But there’s a lot of sex [in our music], a lot of groove,” he qualified.

No, Alison Krauss, Robert Plant and their amazing accompanists didn’t do jazz. Or anything that comes close. However, they guided the immensely enthusiastic crowd gathered at Salle Wilfrid-Pelletier on Friday on a rock journey with vast ramifications, ranging from bluegrass to rockabilly, from pure rock’n’roll to almost mystical flights tinged with country.

There reigns on the two discs of the tandem a nocturnal atmosphere where even the rock impulses are retained. On stage, Friday, it was completely different. We understood from the first two songs (Rich Woman and Fortune Teller, from Raising Sand) that the concert would be quite rock. On the garden side, guitarist JD McPherson led the way wide and heavy. We also note that Robert Plant was in voice.

After a rockabilly detour (the lively Can’t Let Go), it was Alison Krauss’ turn to impose herself on the microphone for The Price of Love, taken from Raise the Roof and borrowed from the Everly Brothers, which she range of his clear voice. Maracas in hand, his venerable 74-year-old sidekick did the backing vocals. It was immediately after that he made his first comment on jazz, a prelude to a Led Zep classic, Rock’n Roll, much less rock than the original (violin intro) and colored with oriental sounds.

The people who had come to see the legend – and there seemed to be many of them in the room – were served: they had the pleasure of hearing some spicy, but always skilfully reinvented interpretations of Robert Plant’s solo pieces (In the Mood), in tandem with Jimmy Page (Please Read the Letter) or with Led Zep (Gallows Pole and The Battle of Evermore). On this last track, Alison Krauss, who took charge of the higher incantatory parts, shone.

Between these two, the current passes as much on stage as on record. The vocals, especially that of Robert Plant, were sometimes a little too forward in the mix, but their communication was almost perfect. The former singer of Led Zeppelin also had the elegance to step back to let his partner reap the light and the applause she deserved. She was superb in Matty Groves, a traditional tune.

Supported by a close-knit and solid group, the two artists offered a rich musical journey, often exciting, skillfully revisiting the past without really trying to make the nostalgic fiber of those who lived the 1970s vibrate. Whether it was rock or not, it was powerful, refined and sometimes even bewitching, like this breathtaking version of When the Levee Breaks, played at the end of the program, before the short encore.

It wasn’t jazz, no. Nevertheless, Robert Plant and Alison Krauss offered a concert of the caliber of those who will mark the history of this festival.