This was the second of two nights for this gig. Opening was The Bar-Kays, who were Otis Redding's backup band when he died in a plane crash that also took the lives of most of the Bar-Kays. In 1972, they appeared at Wattstax:
Next up was local band Tower of Power, out of Oakland. They had already released two albums, which featured songs like "Back on the Streets Again", "Down to the Nightclub", and "You're Still a Young Man". John Wasserman wrote about the Winterland shows in the San Francisco Chronicle. He described Tower of Power (making reference to the "temporary absence of lead singer Rick Stevens," who actually had left the band by then.
Tower of Power’s set was good T of P but not vintage, mainly due to the temporary absence of lead singer Rick Stevens. Good Tower of Power means tight, funky, grinding, pushing, shoving, unrelenting street-corner soul rock with no wasted motion.... In the absence of freedom to dance, however, they are also too even, in terms of sameness of sound, of grinding (the word is more applicable than any other) rhythm section punctured and harassed by horns. “Didn’t they just play that one?” inquired a non-veteran observer as the band cranked into a new song.
You can hear their set at Wolfgang's. Here they are in 1973:
Headlining was Curtis Mayfield. Wasserman again:
Sunday afternoon he received a proclamation from the city of Berkeley and Mayor Warren Widener declared the day as Curtis Mayfield Day. The Rainbow Sign, the Berkeley black art and culture center, stated that “Curtis Mayfield exerts the strongest influence on black youth of any performer in the country today.”
The Sunday night set, which went over an hour and was greeted with great enthusiasm, opened with a soft, sweet “Gimme Some Love” and then marched on through the likes of “Superfly” (gold single), “Love Child,” “Stone Junkie,” “Pusher Man,” “Sure is Funky,” “Stare and Stare” and “Freddie’s Dead” (gold single); a set dominated, obviously by songs from “Superfly,” — songs which discuss the ugly reality of drugs in the ghetto with neither shrill moralizing nor smug acceptance. It is not a life I must live and I don’t relate to it in the manner of those who do. But the descriptions and emotions are plainly valid and perceptive.
Here is Mayfield on Midnight Special in 1973:
And an interview on Soul Train from the same year: