The television ad showed various people shopping, with the screen split three ways to indicate the supermarkets Sainsbury's, Tesco and Asda, before a voice-over said: "Deals. Everywhere aren't they? But wouldn't it be nice if we didn't have to go everywhere to get them?"
The ad said Sainsbury's would compare baskets of £20 or more with prices at Asda and Tesco and offer a coupon for the difference, taking deals into account.
But two viewers pointed out that Brand Match compared the total cost of the branded shop, and any savings on cheaper Sainsbury's products were offset against any items that were cheaper at Tesco or Asda.
The deal meant the value of the coupon was reduced, and customers could have saved more by buying the items at their cheapest price from across the three supermarkets.
Sainsbury's said the ad made it clear that the comparison was of the total price of the branded shop, and believed it contained all the necessary information "for viewers to understand the offer and assess it objectively".
"We considered that the ad ... misleadingly implied consumers did not need to shop around to obtain the full savings from deals, when in fact that was not the case. We therefore concluded the ad was misleading."
The ASA ruled that the ad must not be broadcast again in its current form, and said: "We told Sainsbury's not to state or imply consumers did not need to shop around to fully benefit from deals at Sainsbury's, Tesco and Asda if that was not the case."
A Sainsbury's spokesman said: "We are disappointed with the ASA's ruling since we don't feel their approach accurately reflects the way that customers shop in the real world. We are confident that the millions of customers who benefit from the scheme each month fully understand how Brand Match works.
"However, we have changed the wording of our advertising to reflect the adjudication."