Matthew Schaeffer stars as the Islanders take on the Sharks

No. 1 beat No. 2 and the Islanders got a win over No. 3.

And it wasn’t just two points for Matthew Schaefer’s Islanders over Michael Mesa’s Sharks in the Islanders’ 4-3 win Tuesday night at UBS Arena.

It was, and not for the first time in a season just a few weeks old, a night in which Scheffer seemed to outshine everything else, as he had an assist and a goal, as the crowd chanted his name, where the Islanders could feel completely secure that whatever came of the next 76 games, they had a superstar in the making.

In recording his first point of the night, a secondary assist on Bo Horvat’s power-play goal in the first period, Scheffer extended his point streak to six games, tying Marek Zidlicki’s record for defensemen making career starts and moving him within one point of Alexander Daigle’s expansion-era record for players 18 or younger.

The other two 18-year-olds with six-game point streaks are Sidney Crosby and Wayne Gretzky.

In scoring his second point of the night, a second-period goal that prompted chants to ring out around the UBS stands, Schaefer moved into a tie for the NHL goals lead among defensemen.

It’s rarely been clear that the sky is the limit, and Schaefer is looking forward to reaching it in record time.

On nights like these, everything else seems secondary to a rookie, but the Islanders, whether they win three straight or not, are treading into dangerous territory with their play.

And on Tuesday, as has often been the case this season, the Islanders played a scrappy, scrappy game in their own zone. They lost puck battles. They were wide open defensively and defended the rush poorly.

It’s hard to believe that this can be a winning formula for so long. However, the Islanders are better equipped to fight back than they have been in the past, which is what they did on Tuesday.

After a poor start, the Isles took a 4-2 lead into the final 20 minutes, which they gained after Schaefer tipped in Anthony Duclair’s pass from behind the net at 6:38 of the second.

They didn’t make it easy for themselves from there.

The Islanders came out flabby and ready to absorb pressure in the third period, and San Jose was more than happy to oblige. MacLean Celebrini scored on Dmitry Orlov’s pass at 10:16 of the period to make it 4-3, and Scott Mayfield converted a penalty kick just 25 seconds later.

However, the Islanders did manage to miss the penalty, and with Ilya Sorokin playing his best game of the season with 34 saves, they saw the threat from there.

Schaefer aside, the match wasn’t pretty from the start.

The Islanders started the game brutal, struggling to penetrate or possess the puck and allowing a shorthanded goal to Colin Graf after continuing on the power play. Less than a minute from the end of the game, and with the power play continuing, Bo Horvat tied the score at 1-1 on a low-to-high pass from Matt Barzal.

Mesa, who faced Schafer in a battle between the top two picks in last summer’s draft, scored his first career point, assisting on Adam Gaudette’s 2-2 goal at 14:16 after Casey Cizikas had put the Islanders ahead.

Before halftime, Emil Heinemann made it 3-2 with the Islanders’ second goal of the night, hitting the left post.

Relying on the power play to cover up leaky defensive play is certainly a reflection of the way the Islanders have operated in recent years.

It would be better for the Islanders to be able to fix their defensive issues before needing to answer whether this is sustainable.