The slight sales boost that Memorial Day weekend brought to Broadway mostly evaporated last week, with Rialto cume off about $850,000.

Overall slippage was likely offset somewhat by the fact that the Broadway League, which this week consolidated the reporting of Main Stem numbers, began reporting “gross gross” vs. the traditional net gross (which subtracts credit card transaction fees from totals).

Down about 4%, the week’s tally hit $19.6 million for 32 shows on the boards — while over the same frame in 2008, sales fell more than $3 million (15%) to $17.5 million for 34 productions playing.

“Joe Turner’s Come and Gone” ($283,197) — the most talked-about offering of the weekend, thanks to a highly publicized Saturday night visit by President Obama and first lady Michelle Obama — didn’t climb by a huge amount, but the coming weeks will indicate whether the recent publicity will lead to a sustained increase in sales at the Lincoln Center Theater production.

All the members of the millionaires’ club — including “Wicked” ($1,552,347), “West Side Story” ($1,305,829) and “Billy Elliot” ($1,253,482) — rose, as did hot-ticket play “God of Carnage” ($911,320), surpassing the $900,000 mark.

“Blithe Spirit” ($481,117), off about $110,000, took the heftiest hit of the week, while “Shrek the Musical” ($673,539), whose producers just announced a summer discounting plan, fell by about $100,000.

Also among the tuners to slip were current Tony nominees “Hair” ($866,759) and “9 to 5” ($755,755). New tuner contenders “Rock of Ages” ($498,357) and “Next to Normal” ($357,110), on the other hand, continued to gain momentum.

Two play productions currently pulling out all the stops to attract auds, “The Norman Conquests” ($297,206) and “Reasons to Be Pretty” ($168,207), were both down slightly.

Also contributing to the overall decline was the absence of two shows that closed May 24, “Desire Under the Elms” and “33 Variations.”