Marcos stormed back from a set down to defeat wild card Dustin Brown 4-6, 7-6(4), 6-4 and book his spot in the ASB Classic quarter-finals on Wednesday.
Into his first ATP World Tour quarter-final since advancing to the semis on the grass of Newport in July, Marcos needed two hours and six minutes to overcome Brown. He fired 12 aces and saved eight of 10 break points faced, extending his head-to-head edge to 5-0 over the German.
Marcos was greeted by daughter Zahara on the court following the match. "It is good for her and good for us as parents to share this," he said. "Dustin is an incredible talent. The conditions are different during the day, but I'm happy I'm through and we have another match tomorrow."
Marcos had his back against the wall deep in the deciding set, facing 0/40 on his serve at 4-all. But he would dig deep to deny four break points and converted his third match point in the next game to notch the victory. He prevailed when a Brown forehand approach sailed long.
Marcos will next face Jiri Vesely, with a spot in the final four on the line. He has yet to lose to the Czech, claiming all three of their previous encounters. They most recently faced off at the ATP World Tour Masters 1000 event in Indian Wells two years ago.