A method of reducing network congestion and service latency associated with downloading Web pages containing third party advertisements. In one embodiment, pattern recognition algorithms are employed to determine whether a request for a URL may be satisfied by the content associated with a URL which is contained in the client's cache; if there is a pattern match, the cached contents associated with the URL are delivered to the browser to satisfy the request. In another embodiment, images associated with HTML snippet ads are requested and cached by client software before they are requested by the browser downloading the Web page where the images will be displayed. In a third embodiment, latency is reduced by "time shifting," wherein a cached ad is displayed while client software requests and caches the ad originally requested ad, which will be shown the next time the URL is requested. In other embodiments, this time-shifting technique may also be combined with the pattern-recognition technique and the approach to accelerating delivery of HTML snippet ads.