Mertens was ahead in the second set with 5-2 but went on to lose 9 straight sets to go to 4-0 down in the second.
Speaking on Eurosport Wilander said, "I think that Serena looks good and she has worked hard, she looks fitter than she did in Paris".
He later apologised, saying: "If somebody feels offended, I say sorry".
Suarez Navarro, ranked 31 in the world and one of the smaller players on tour, lacks the big weapons and serving power needed for grass and has always had trouble against Williams.
The 37-year-old American, who is still on course for her 24th Grand Slam singles title after beating Carla Suarez Navarro 6-2 6-2 to reach the quarter-finals, said she was also pleased she had learned to avoid hitting the ball on the wrong side of the net.
Serena reacted exuberantly to a driven forehand victor that saw off another service wobble to set up a hold at 4-2 and a glorious cross-court backhand to break for a fifth time in the contest meant Suarez Navarro's race was run.
The All England Club is the only Grand Slam site where there is no play planned for the tournament's middle Sunday - and the only one where everyone still around plays on the initial day of Week 2. She will be facing Serena Williams in the quarter-finals.
"She's a fighter on the court".
"(Alison) is a great person, she is a fighter on the court and she is playing really great. "She doesn't let anything limit her", she said. But at the same time it does look like she gets nervous, she starts slowly - how does that happen after you've warmed up?
Global shares fall as prospect of sharp USA rate cut fades
Strong U.S.jobs data on Friday reduced market expectations for rate cuts from the U.S. central bank at its next meeting in July. -China trade dispute had helped Wall Street's main indexes rebound from a slump in May and hit record highs last week.