Bafana - ranked 73rd in the FIFA world rankings - were held away from home by the lowly 108th ranked Warriors in a tense encounter.
Tau, newly named as vice-captain was hauled off in the 78th minute after failing to inspire Bafana to register an all-important away goal.
Broos admitted that the 26-year-old's match-fitness played a factor in his display and as to why he was substituted.
"Percy I don't think at the moment is in his best shape," Broos said post-match.
"This is normal and you could see that he missed the tempo of the game so that is something for him also to work on over the next few weeks.
"But he remains a good player and why he stayed so long on the pitch. I hope for the next games in October and November we will have a much-improved Percy Tau than we have at the moment.
The Belgian also lamented his side's attacking threat as they failed to register a win against a weakened Warriors side without as many as 13 first-team stars.
"You have to score to win games," Broos said post-match.
"Today it was not so good offensively and I think we have to work on that in the next weeks and months.
"To win, you have to score and this was a problem for us today."
Bafana next host the Black Stars in their second Group G qualifier at the FNB Stadium on Monday.
Kick-off is at 18:00.
Zimbabwe: Shumba, Lunga, Chimwemwe, Mudimu, Bhasera, Kamusoko, Munetsi, Mahachi, Billiat, Kadewere, Musona.
Substitutes: Arubi, Madhananga, Mapisa, Murwira, Moyo, Rusike, Dzvukamanja, Fabisch, Wadi, Songani, Stima, Chikwende.
Bafana Bafana: Williams, Morena, De Reuck , Xulu, Mobbie, Mvala, Mokoena, Tau, Links, Singh, Makgopa
Substitutes: Mothwa, Bvuma, Blom, Dube, Ngcobo, Brooks, Maart, Mbule, Hlongwane, Letsoalo.