FOXBOROUGH, Mass. — Before you read anything into the fact that Jimmy Garoppolo was the first quarterback off the bench to take over for Tom Brady Friday night in the New England Patriots’ 42-35 preseason victory over the Philadelphia Eagles, consider this:

Ryan Mallett, the incumbent backup, missed two days of practice this week – the two joint practices against the Eagles – because of an undisclosed injury.

Or so we think.

The Patriots are tight-lipped when it comes to injuries. But Mallett certainly appeared to injure his left knee while awkwardly sliding in last week’s preseason game in Washington.

So Garoppolo got the call first Friday night – and once again he gave everyone something to think about.

He looked cool and poised in his first two drives, each resulting in a touchdown pass. He completed four of his first five passes and finished 6 of 12 for 72 yards and the aforementioned touchdowns, a 15-yarder to James Develin on a swing pass and a 4-yard fastball to Brandon LaFell in the back of the end zone.

And then Mallett came in to start the second half and reminded everyone to calm down.

Playing with the reserves’ reserves – the guys trying to make the Patriots’ 53-man roster – Mallett had a very strong second half, running for a touchdown, throwing for a touchdown and showing the arm that everyone thought would make him a first-round selection when he came out of the University of Arkansas.

Of course, Mallett didn’t get picked in the first round – too many off-the-field questions – and fell to the Patriots in the third round, with the 74th pick in the 2011 draft.

Garoppolo was a surprise second-round pick in May, taken with the 62nd pick. He was immediately tabbed as Brady’s heir, and Mallett was labeled as trade bait.

Well, here we are two games into the preseason and nothing much has been settled.

Mallett didn’t look good in the preseason opener against Washington, while Garoppolo popped onto the scene.

Against the Eagles, both showed a command of the offense, in different ways. Garoppolo, who struggled mightily the first couple weeks of training camp, is more mobile and used that to complete a couple passes. Mallett has a strong arm and displayed a nice touch on a couple throws. He finished with seven completions in 11 attempts for 92 yards, the touchdown a 17-yarder to Brian Tyms.

And the starter, Brady? All he did was show the boys how it’s done: 8-of-10 passing for 81 yards and a touchdown, a beautiful back-shoulder throw to Kenbrell Thompkins for 15 yards. He also threw an interception, which was returned 77 yards for a touchdown by Patriots hater Cary Williams.

Before you ask why we should even care who backs up Tom Terrific, think back to the 2008 season. Brady threw 11 passes, then was lost for the season because of a knee injury in the first quarter of the first game. Matt Cassel, who was a backup at USC to both Carson Palmer and Matt Leinart, led the Patriots to 11 wins. He then turned that season into a big contract and starting job with the Kansas City Chiefs.

Mallett certainly improved his trade value with his performance Friday night, and Garoppolo proved he can move an offense against good defensive players.

But the Patriots won’t make a rash decision. Don’t be surprised if they keep both, to allow Garoppolo to learn under both Brady and Mallett.

Bill Belichick, of course, was non-committal about any of his quarterbacks after the game: “I thought all three of our quarterbacks handled themselves pretty well. There weren’t a lot of major problems.”

The fact is, a good backup quarterback is gold in the NFL.

And the Patriots have two more chances to figure out who theirs will be.