Forlan scored twice in an many minutes in the first half to put his side in control at the break, with Suarez at the heart of both before adding a third himself early in the second period.
Japan fought bravely and were able to cut the deficit through Shinji Kagawa but Alvaro Rodriguez restored the visitors' three-goal cushion, before Keisuke Honda fired an inch-perfect free kick into the top corner to make it 4-2.
The deadlock was broken just before the half-hour mark when Liverpool forward Suarez broke Japan's offside trap down the left-hand side.
He raced away from the home defenders into the penalty area and drew the goalkeeper out before cutting back to his strike partner Forlan, who had the simple task of putting it into the open goal.
And when Suarez was fouled 25 yards from shortly after, Forlan curled a brilliant free-kick over the wall and into the top corner, wrong footing the keeper in the process.
Uruguay led 3-0 seven minutes after the interval as Suarez finally got his name on the scoresheet.
A cross from the right hit a Japan defender, and as the ball dropped free inside the penalty area, the 26-year-old pounced to fire it into the back of the net.
The hosts pulled a goal back almost immediately after some less than impressive defending from Uruguay.
A chipped pass from Honda evaded two defenders and the goalkeeper, leaving Manchester United playmaker Kagawa with a simple tap in from five yards.
Gonzalez then met a looping cross from Cristian Rodriguez to head into an unguarded net, before Honda's fantastic strike in the 71st minute completed the scoring.
‘The pure simplicity of the way Slot has managed the squad is probably the biggest thing I could say about him. It’s not broken, so let’s get on with it’: Liverpool legend full of admiration for Jurgen Klopp's successor at Anfield
‘I trained at Spurs and thought they’d give me a chance. But I received a letter thanking me but saying they didn’t think I was good enough – I was gutted’: How Tottenham missed out on signing Wales legend John Toshack
