Shapovalov was outclassed 6-2 6-4 by former US Open victor Juan Martin del Potro in Wednesday's Classic second round, and will now head to Melbourne.
Defending champion Sock lost in only 61 minutes to his German opponent, who is ranked 65th in the world.
Cutting a slightly lumbering figure, del Potro was nevertheless effective against the young gun Shapovalov, who made too many unforced errors.
He cruised through a first-set tiebreaker after both players could not break serve, before seizing the initiative at the start of the second set.
Del Potro struck in the first game to break but was forced to repeat the feat in the seventh game after Ferrer had levelled matters at 3-3.
"I had luck to break his serves twice and that's it, then I held my serve in all the second set, saving break points, playing good tennis down the line, and I had to take a risk playing against David because he's a fighter", del Potro said.
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"But I've been working hard to play this tennis and hopefully I can still improve in the next matches".
Mertens will play Mihaela Buzarnescu of Romania, who has reached her maiden WTA final.
But with all three sets going to a tiebreak, Bautista Agut's relentless accuracy and fitness came to the fore, helping him win in just under three hours.
Bautista Agut booked his spot in the Classic final with a 6-7 (7-9) 7-6 (7-3) 7-6 (7-5) win over the journeyman Haase, battling from beginning to end. "If I play well maybe I have a little chance".
"I was a break up in every set and right after I got (it), he breaks back".
"I passed really bad moments on the court and in that moment, I scream because I was very stressed", the world No.21 Bautista Agut said.