Two Premier League title rivals identified the central striking berth in their respective sides to be in need of reinforcement over the summer.
United had set their sights on Morata at one stage, while Lukaku was being heavily linked with a return to Stamford Bridge for a second spell.
The Belgian was, however, to move to Old Trafford from Everton for £75 million while Morata traded Real Madrid for west London – with both having settled quickly in new surroundings to open their goal account early and offer an immediate return on the investment made in them.
Pressed for his opinion on two leading marksmen, former Chelsea defender Le Saux told Betfair: "Alvaro Morata has shone in those two games [against Everton and Leicester], scoring in each.
"Chelsea were obviously in for Romelu Lukaku in the summer and missed out, but Morata is certainly doing enough to justify his transfer fee.
"At the moment you might say that Lukaku is the better striker, based on amount of goals scored, but Morata has huge potential.
"His movement is exceptional, and offers a different challenge to his predecessor at Chelsea, Diego Costa – who has tormented Arsenal in recent seasons – as he likes to get away from players and into space where he can do the damage.
"A few people in the summer questioned whether he would score goals in the Premier League but he has already proven them wrong which must delight everyone at Stamford Bridge."
Morata was brought in to fill the void created by the decision to move on from Costa – although the AWOL Spain international remains on Chelsea’s books after failing to secure a summer switch.
He will be hoping to lead the line again on Sunday when Arsenal make the short journey to Stamford Bridge, while Lukaku will be seeking to upstage his predecessor at United when Wayne Rooney and Everton pay a visit to Old Trafford.