Raza made a crucial 39 runs on Sunday and lifted Zimbabwe from a precarious 7-125 to 205 all out by sharing a 62-run eighth wicket stand with No.9 batter Richard Ngarava, who top-scored with 48.
Under overcast conditions, Raza (2-7) picked up two wickets in one over as Pakistan limped to 6-60 in 21 overs before it rained and denied further play as Zimbabwe took a 1-0 lead in the three-match series.
Pakistan's second-string new ball bowlers – debutant Aamer Jamal and Mohammad Hasnain – couldn't make an impact on Zimbabwe's openers after the visitors had rested frontline pacers Shaheen Shah Afridi and Naseem Shah for the series.
Pakistan also rested ace batter Babar Azam for the first time in an ODI since 2019 as they experimented ahead of next year's Champions Trophy.
Tadiwanashe Marumani (29) flicked Jamal to square leg for a six and Joylord Gumbie (15) hit three fours against the seamers as they combined in a better than run-a-ball opening stand of 40 runs against a wayward Pakistan attack.
Gumbie got run out in a mix-up with Marumani in the sixth over before Pakistan came back hard through their spinners.
One of the three Pakistan debutants, left-arm wrist-spinner Faisal Akram took 3-24 and vice-captain Salman Ali Agha claimed 3-42 as Zimbabwe slipped to 7-125 in the 26th over.
However, Ngarava and Raza thwarted Pakistan's spinners and pacers alike in a 69-ball stand to give the total respectability.
Raza perished when he tried an expansive hit against Akram and was caught on the boundary while Ngarava was the last man out, after hitting five fours and a six, when he chopped Hasnain onto his stumps.
Fast bowler Blessing Muzarabani used the home conditions to perfection and snared the early wickets of Saim Ayub (11) and Abdullah Shafique (1), both caught behind inside the first three overs.
Kamran Ghulam (17) and skipper Mohammad Rizwan (19 not out) couldn't pace the chase before Pakistan lost four wickets in the space of 18 runs against the spinners.
Ghulam tried to break the shackles but Sean Williams (2-12) got a thick edge and earned Marumani his third catch behind the wickets before Raza had two in three balls.
Raza pinned Salman lbw and one ball later Haseebullah Khan was out for zero in his ODI debut when he played the wrong line.
The three-match ODI series will be followed by three T20s with Bulawayo hosting all the matches.
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