Leon Cameron says his team should have put Melbourne away in the third quarter of Saturday's clash at the MCG, but wasted a golden opportunity.

The GIANTS were pipped by two points in a thrilling round one clash, and were left to rue their wastefulness in attack, having kicked 2.6 in the third quarter to the Demons' 1.1.

When Melbourne got its opportunity in the final term it made the GIANTS pay, quickly pegging back a 21-point deficit and delivering a valuable lesson.

"Our boys have to learn that everything counts in this game, because if you don't take your opportunities someone will take four points off you," Cameron said.

"It's a tough loss. Whether we deserved to win or we deserved to lose, the end result is they’ve got four points and we've got zero. 

"In the third quarter we dominated and could have put the game away, but we didn't and when they had a chance to put the game away they did." 

Among the culprits in the third term were revered finishers Steve Johnson and Devon Smith, and midfielder Lachie Whitfield. Toby Greene and Caleb Marchbank also missed chances in the dying minutes of the last quarter.

Johnson finished with 2.2 and 23 possessions in his first match for GWS, but Cameron alluded to a number of opportunities the premiership star had to share the ball that he didn't take.

"There were definitely some decisions that he will look back and say 'I have to be better'," Cameron said. 

"He had an interrupted week where he was a bit crook, but he's such a competitor … he had a fair bit of the ball and he's obviously kicked a couple.

"Small forwards like that, if they kick a couple of goals every week you give them a tick."

The coach was pleased with young tall Rory Lobb, who was also among the GIANTS’ wasteful forwards with 2.3, but proved crucial to their forward set-up with 15 possessions and four contested marks.  

With key forward Jeremy Cameron sidelined for a further three matches through suspension, Jon Patton could return against Geelong in round two after booting five goals in a NEAFL practice match on Saturday. 

Patton has endured two knee reconstructions and suffered patellar tendinopathy, and Cameron said he would wait for the 2011 No.1 draft pick to declare he was ready to make his AFL return.   

"He knows that might be weeks away, but when he comes in he wants to be confident in himself," the coach said.   

"And I think he wants to be confident so his teammates are confident. 

"It sounds pretty good what he's done (on Saturday) and I'm rapt he's taken another good step.

"We know that 2014 he was a very exciting prospect for us. Our job is to hopefully get him back to where he was heading."