Waqar took four early wickets in a burst of 25 balls to put Zimbabwe in deep trouble at 29 for 4, while Saqlain achieved a career-best 5 for 32 to wipe out the middle and tail. The left-hander Andrew Flower remained not out, adding 60.
Pakistan's bid to level the series had suffered an early blow when their captain, Aamir Sohail, pulled out before the start citing a severe headache and fever, although sources later suggested he walked out following a row with selectors.
The wicketkeeper Moin Khan replaced Sohail as captain, won the toss and sent Zimbabwe in on a grassy pitch.
Waqar struck with the first ball of his second over, dismissing Gavin Rennie for three. Murray Goodwin was next to go with his score on 10, edging an outswinger from Waqar to Moin.
Zimbabwe's captain Alistair Campbell started with a boundary but could not keep a short-pitched ball from Waqar down and was caught by Yousuf Yohanna for five.
Waqar then trapped the opener Grant Flower lbw for seven to put Zimbabwe in grave trouble at 29 for 4. He took 4 for 18 in a devastating first spell and gave Pakistan the advantage they held at the close.
"Its a good beginning for me because we won the crucial toss and hopefully our batsmen will give us a good total to force the win," Moin said.
First day; Pakistan won toss
ZIMBABWE - First Innings
G J Rennie c Ijaz b Waqar 3
G W Flower lbw b Waqar 7
M Goodwin c Moin b Waqar 10
*A D R Campbell c Yousaf b Waqar 5
A Flower not out 60
N Johnson c and b Shoaib 14
C Wishart c Salim b Saqlain 28
H H Streak c Wasim b Saqlain 19
H K Olanga c Shoaib b Saqlain 3
A Huckle c Saeed b Saqlain 13
M Mbangwa c Ijaz b Saqlain 2
Extras (b4, lb3, nb12) 19
Fall: 1-3, 2-16, 3-22, 4-28, 5-55, 6-104, 7-136, 8-140, 9-170.
Bowling: Wasim Akram 20-6-42-0; Waqar Younis 18-3-54-4; Shoaib Akhtar 15-1-48-1; Saqlain Mushtaq 13.5-3-32-5.