Good thing Nintendo’s Wii console is selling so well. The company will need some of that money to pay a hefty legal bill.

On Thursday, the market research firm NPD Group reported that Nintendo sold an amazing 714,000 Wiis nationwide in April alone despite it being a traditionally slow time for game and console sales. That stellar number far exceeded same-period sales for rival systems PlayStation 3 and Xbox 360.

Those systems sold 188,000 units and 187,000 units respectively, NPD says.

Even Nintendo’s handheld system, the DS, outperformed the big boys, selling 415,000 units last month — or twice the volume of rival handheld PlayStation Portable.

At this rate, Wii will outsell Xbox 360 in no time — perhaps this month. Microsoft said Wednesday its console became the first to sell 10 million units, but NPD figures Nintendo has sold only 500,000 fewer Wiis than that.

Next week, Nintendo releases “Wii Fit,” an exercise-oriented game with a balance board peripheral and considered a hotter ticket than “Grand Theft Auto IV.” Most retailers already are reporting that their inventories are sold out, and even the Nintendo World Store has stopped taking pre-orders.

All this good news and anticipation likely is a relief to Nintendo bean counters, who this week learned the company owes a $21 million debt courtesy of a 2006 patent infringement suit it lost to a small east Texas gaming company.

A federal court ruled Wednesday that the design of some Nintendo console controllers — specifically, the Gamecube, Wii Classic and WaveBird controllers –violated patents already held by Anascape, based in Tyler. A separate suit filed against Microsoft for similar reasons was settled out of court for an unspecified amount.

The Nintendo case does not involve Wii’s motion-sensitive controller.

Of course, Goliath hasn’t finished fighting David. Though lawyers for both sides declined to comment, a Nintendo spokesman told The Associated Press the company intends to press an appeal and expects Anascape’s award to be reduced “significantly.”

Game Guy doesn’t understand why. Given the Wii’s boundless popularity and booming sales, Nintendo probably could scrape up $21 million in change from under its sofa cushions.