There’s a reason why pencils have erasers.

As much as we like to construct line combinations for the Vancouver Canucks, pre-season performances — both good and bad — have a way of messing up the process. And so do injuries.

The Canucks are without left winger Nils Hoglander, who’s out three to four weeks with an ankle injury suffered against the Calgary Flames on Wednesday in Abbotsford. On Sunday in Edmonton, veteran right winger Conor Garland didn’t take the warm-up skate and sat out with what the team has been calling a ‘minor issue’.

If Sunday was the season opener, Garland likely would have played.

What the absences have done is sharpen the focus on who’s under the microscope for roster positioning. Hoglander was likely a third-liner but now Drew O’Connor, who was destined for the fourth line, was skating impressively with rookie centre Braeden Cootes and right winger Jonathan Lekkerimaki on Sunday.

It was a good top-six mix test with the Oilers’ two-headed monster of Connor McDavid and Leon Draisaitl in full flight. They needed just 1:28 to combine on the opening goal in a 4-3 victory and it was a wake-up call for younger Canucks wondering about pace of play with superstars on the ice.

Draisaitl had four points (2-2) and McDavid three (1-2).

Meanwhile, O’Connor is intriguing because he showed upon arrival last season in a trade that he can move well for a big winger and make plays through the neutral zone and be heavy on the forecheck. On Sunday, he quickly meshed with his linemates, was involved in the offensive zone, and got to the net with purpose.

Might be a nice fit with the feisty Kiefer Sherwood on the third line to play hard, be responsible and be good in transition. O’Connor got to the net in the third and a Cootes shot went off an Oiler with O’Connor causing havoc. And two goals in 43 seconds narrowed the deficit to 3-2.

Playing with the creative Cootes has elevated O’Connor’s game and the 18-year-old Cootes continues to impress.

He’s trying to do what Burnaby native Ryan Nugent-Hopkins did in 2011 as the first overall pick in the NHL draft. He had 58 points (18-34) in 62 Oiler games as a rookie. Cootes is striving to start the season in Vancouver and might get some games. He’s been that noticeable. He also won six of 11 draws Sunday.

“He’s getting better every day,” said Canucks general manager Patrik Allvin. “Fits in well and plays hard with a hockey I.Q. He keeps earning days.”

Maybe the Canucks carry 14 forwards and seven defencemen this season. Aatu Raty and Jonathan Lekkerimaki had the other Canucks goals and the third-period rally was inspiring.

“They had a lot of their lineup in and they’re a really good team,” said Cootes, a Sherwood Park, Alta. native who had a big throng of support. “We had younger guys and fought hard and kind of took over the third period and almost got it to overtime. You get more comfortable as you get to know guys.

“It feels more normal and gets easier every game.”

Said Canucks head coach Adam Foote: “I loved the effort. We didn’t quit and we outscored them 3-1 in the third. They applied a lot of what we’ve been working on and it started to turn our way. We had confidence and made offensive plays.”

Here is the report card from Sunday’s game:

Drew O’Connor (B)

Tracked down puck in high slot in first period, got good backhander away. Then spun in mid-air and knocked loose puck down and just wide of net. One-timer on net at end of second period. Nose for the net.

Braeden Cootes (B)

Head was always up. Got by sideboards check and set up O’Connor for chance in first. So fast. So smart. Didn’t dip his toes in against a veteran lineup. That said something. Was also targeted physically. Sucked it up.

Filip Chytil (B+)

Played at speed early and often. Spun and had backhander go off side of net. Went end to end on another rush by gaining zone through neutral zone. Took O-zone penalty, then came out of box to take long feed right to net. Puck then slid off his stick. Won 11 of 19 draws.

Arshdeep Bains (B)

Used strength, speed and smarts to hold off defender and shovel puck to Chytil at top of crease in second period. Such good game awareness. Tipped puck on net from his knees while driving net.

Jonathan Lekkerimaki (B)

That shot was on display on power play. With quick flick of wrist it whistled just wide of the net. It’s a weapon. Took a cross-ice feed from Chytil in third and drilled one-timer home. Then let another one fly. Still, total game must be focus.

“We tried our best and battled to the end,” said Lekkerimaki. “We wanted the win and I just tried to find my shot.”

Max Sasson (B)

Smart defensive zone awareness to deny Oilers top line. Put second period backhander off crossbar. Good chance early in third by winning battle. Gave good honest effort.

Aatu Raty (B-)

Was having quiet night for a guy pencilled in as third-line centre. Drew a penalty, but wasn’t good in circle and foot speed was an issue. Then snapped one home high on the short side.

Kiefer Sherwood (B)

Moving the puck and moving the opposition. Sherwood knows his value. Bowled over Ty Emberson in neutral zone and had four hits in first period and eight overall. Added four shots.

Linus Karlsson (C)

We keeping looking for more at this level. Coming off strong AHL season and Calder Cup presence, you like to think a fourth line right-wing spot is waiting. But Karlsson has to earn it. Not waiver exempt. Had three shots Sunday.

Nils Aman (B-)

Played like the responsible depth guy he is. Nothing fancy. Got to net for chance in second period and hustled on backcheck to cover for defender.

Mackenzie MacEachern (C)

Played 9:39 on fourth line as replacement for injured Garland. Hard to evaluate. Didn’t hurt club.

Joe LaBate (C)

Added bite with a presence and willing to scrap. Laid heavy second period hit on Atro Leppanen with crunching sideboards hit. Had three hits. Adds depth to organization.

Thatcher Demko (B-)

Lost positioning, stick on opening goal. Recovered and sharp on redirect before stare down as McDavid tried to deke to backhand at side of net. Toe drag by Leppanen forced calm and positioning. A little late with push off on Draisaitl rocket to get to far post. Acrobatic save in third kept it 3-2 before another Draisaitl snipe.

Marcus Pettersson (B)

Dove in first period to knock puck away from Nugent-Hopkins and worked well in pairing with Elias Pettersson. Blocked three shots with smart positioning. Veteran savvy showed.

Elias Pettersson (B)

Had heavy point shot north of 90 m.p.h. go through a maze and right on net. Kid doesn’t flinch in any situation. He gets it. Very mature.

Derek Forbort (C+)

Lost stick and positioning on first goal and allowed Trent Frederic to gain position for screen and jam home loose puck. Joined rush in second with O’Connor but pushed Stuart Skinner’s pad back on disallowed goal. Kudos for effort.

Filip Hronek (B)

You often don’t notice the wily veteran because he makes right play at the right time. Delivered hit on Raty goal. Finished with two assists and logged a whopping 27:10 of ice time.

Pierre-Olivier Joseph (B-)

Has struggled with positioning, but made good move in first period. Off a turnover in high slot, drilled a 90.3 mph slapper past the glove of Skinner and off the post.

Kirill Kudryavtsev (C)

Reached with stick in D-zone coverage scramble and took second period minor. Draisatil quickly responded with one-timer howitzer over Demko’s shoulder to make it 3-0. Learned a lesson.

bkuzma@postmedia.com