I’ve been watching the World Cup for four decades, and this is the most exciting and enthralling I’ve seen.

Group play averaged more goals per game than any tournament since 1958. Just 17 percent of matches finished in a draw, and nearly half of the first-round contests were decided by a single goal. Seven games were settled by a goal in the last five minutes.

The textbook has not just been ripped up and tossed out the window — it’s been pulverized, shredded and rocketed to Mars.

Four countries ranked in the world top 10 have been sent packing: Spain, Italy, England and Portugal. One is the defending champion, another two have won the trophy five times between them and the last has the best player on Earth.

They have gone home, but Nigeria, which barely scraped into the top 50, is still there. For the first time ever, we have two African countries and three from North and Central America in the last 16.

Away from the action, we’ve had Chewy Luis sink his teeth into an opponent, a plane carrying $3 million in cash to pay players, two teammates fighting each other during a game and Nigeria refusing to practice after an argument over unpaid bonuses.

And things are about to heat up.

Although now it’s sudden death — win or go home, as they say — paradoxically that may stifle the action. At this level, many games turn on one flash of brilliance or an individual error, and that can constrain players, who are frightened of making the mistake that lets down their whole nation. But hopefully the wonderful attacking soccer will continue, and this will go down as one of the best World Cups ever.

The first knockout stage has thrown up some intriguing contests.

On Saturday, it’s the turn of the flamboyant South Americans, all but one of whom made it through the groups. Brazil has stuttered somewhat and been overreliant on star striker Neymar, while Chile has been a revelation, dismantling the Spanish with a tactical counter-attacking master class. But Brazil still has the quality to defeat their neighbors for the third tournament running.

That’s followed by Colombia vs. Uruguay. Colombia has impressively won all three games, but that was in a weak group. Thanks to Luis Suarez’s chomping moment of madness — the third of his career — the Uruguayans have been stripped of their outstanding forward and (dare I say it) up front they will lack bite.

On Sunday, Mexico plays the Netherlands, which also has won all three matches but in a much tougher group. Robin Van Persie and Arjen Robben have led the line superbly, and the Dutch will be relying on them to breech a resilient Mexico defense that battled to a goalless tie with Brazil.

The weekend ends with the contest that no one predicted when Costa Rica lines up against Greece on Sunday. Costa Rica has been the biggest shock in a tournament of shocks; its topping a section containing three former winners was the outstanding performance of the first round. Neutral fans will cheer them on against a dull Greece team that neither scores nor concedes many goals, so don’t be surprised if this one goes to penalty kicks.

Nigeria is the lowest-ranked country left, and it would be a huge surprise if it knocks out the free-flowing and free-scoring French on Monday.

The other game that day is a repeat of one of the most famous contests in World Cup history. Back in 1982, Algeria sent shock waves through the global soccer community when it defeated West Germany 2-1, but that was all for naught when the Germans carved up a result with Austria that saw both teams progress. They have waited 32 years for revenge. No one else will be as fired up as the Desert Foxes, and although everyone who remembers that game would love them to do it, it’s hard to see them defeating the second-best team in the world.

This round finishes Tuesday. In theory, fifth-ranked Argentina facing Switzerland, rated sixth in the world, is the closest game of the round. Most experts have the South Americans breezing through this, but they have struggled, with moments of Lionel Messi magic bailing them out against Iran and Bosnia. The Swiss have lost just a handful of competitive matches in the past few years and will be difficult to break down, so expect this to be closer than many predict.

And to finish … oh, yes, the United States vs. Belgium. I think that game is worth examining in a bit more detail next week, don’t you?