Swindon winger Joel Cotterill scored the only goal of the contest when his finish deflected past Tommy Simkin in the 59th-minute.
Their lead at the top has been cut to four points after Swindon put paid to their 12-match unbeaten run on home soil in League Two.
Mat Sadler named the same XI that drew 2-2 at Cheltenham Town on Tuesday, with Brandon Comley starting on his 100th appearance for the club.
Ian Holloway made just one change for the visitors as Tom Nichols was preferred to Jake Cain in attacking midfield.
Neither side managed to stamp their authority on proceedings during the opening half-hour although Walsall did have a few bright moments.
Jamille Matt won the second ball on the halfway line and laid the ball back for Comley to find Jamie Jellis in a pocket of space. Connor Barrett was released down the right but his low cross was cleared with Ellis Harrison lurking with intent at the back post.
Will Wright created the two best openings for Swindon during the opening exchanges with free-kicks from deep. He chipped his first into the inside-left channel for Harry Smith to creep in behind Oisin McEntee and lift over from an acute angle on the half-volley.
Shortly after, his diagonal ball was brought down nicely by Joel McGregor on the right. The teenager spun Liam Gordon on the edge of the box, only for David Okagbue to stick out a vital leg and prevent his low cross from finding Smith inside the six-yard box.
At the other end, Jellis forced a smart save from Swindon goalkeeper Connor Ripley with a flicked header at the near post from Taylor Allen’s corner.
Walsall tailed off somewhat for a 10-minute period and were guilty of giving up the ball on a number of occasions in the centre of the park.
Swindon failed to capitalise and Ryan Stirk tried his luck from distance when he drove a low effort wide of Ripley’s right-hand post.
Okagbue rescued Walsall from falling behind on the cusp of half-time. Cotterill raced into the box after latching on to a smart through ball by Gavin Kilkenny but the Irish defender got across in the nick of time to divert behind on the slide.
After the break, Matt hooked an audacious overhead kick wide of the target after Jellis’ long throw was flicked on by McEntee at the near post.
But Walsall fell behind less than a minute later when Cotterill opened the scoring just before the hour-mark.
Tshimanga snuck in behind Allen but was stopped in his tracks by a flying block from McEntee. Cotterill pounced on the second ball and fired his finish beyond the reach of Simkin with the aid of a deflection.
Wide man Tshimanga came to life in the second half and caused serious problems, especially for Barrett. His stabbed effort from close-range was saved by Simkin and he forced the Walsall goalkeeper into action again after cutting inside against Barrett and unleashing a powerful strike towards the near post.
Sadler introduced Albert Adomah and Levi Amantchi, before adding Danny Johnson to the attack for the final 10 minutes.
Adomah had the two best chances after Walsall fell behind. The 37-year-old fired a low shot into Ripley’s midriff and stung the palms of the Swindon goalkeeper at his near post after racing on to a through ball from Jellis.
Adomah picked up a loose ball just outside the penalty area but could only shoot into Ripley’s midriff with a low drive. The 37-year-old, hunting for his 100th professional club goal, was then teed up by Jellis in the closing stages and stung the palms of Ripley at his near post.
Next, Walsall make the trip to Prunton Park to face Carlisle United on Tuesday night.
TeamsÂ
Walsall (3-1-4-2): Simkin; McEntee, Okagbue, Allen; Comley (Lakin 59); Barrett (Johnson 80), Jellis, Stirk, L Gordon; Matt (Amantchi 73), Harrison (Adomah 73).
Unused: Hornby, Williams, Weir.
Swindon (4-3-3): Ripley; McGregor, Clarke (Sobowale 80), Wright, Freckleton; Kilkenny, Ofoborh; Cotterill (Glatzel 80), Nichols, Tshimanaga (Payne 90 +1); Smith.
Unused: Bycroft, Ameen, Westley, Butterworth, Cain.
Referee: Paul Howard
Attendance: 6,910
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