The Swiss star held off local hero Gerhard Kerschbaumer at Val di Sole in Italy, while Poland's Włoszczowska kept Canadian Emily Batty at bay in a riveting women's race. Here is all you need to know:
The women's race got off to a dramatic start as Danish title leader Annika Langvad, who won the XCC short track race earlier in the weekend, was out early injured.
Current world champion Jolanda Neff, France's Pauline Ferrand-Prévot and Włoszczowska broke free with Batty joining the trio later in search of her first World Cup win.
Ferrand-Prévot faded first then Switzerland's Neff lost momentum on one of the final climbs with Batty leaving her charge too late to catch Włoszczowska at the line.
Neff ended third and Ferrand-Prévot fourth with Norwegian Gunn-Rita Dahle Flesjå the oldest rider to finish on a WC podium aged 45 - her 70th in total.
Włoszczowska was left to celebrate her first XCO World Cup win since 2012 after a series of podiums including XCO silver at the Rio Summer Games in 2016.
The 34-year-old said: "It means that I am still young and powerful! I was feeling better and better the more the race went on. Focus and don't make any mistakes. Push hard until the end and don't think about the result."
Batty, 30, revealed: "I was just chasing and turning myself inside out trying to bring Maja back. Few seconds short this week. I was so damn close to that win."
Reigning men's champion Schurter was beaten by Dutchman Mathieu van der Poel in the short track race and broke away to leave his main rivals eating dust.
Italian Kerschbaumer, though, wanted to put a smile on his fans' faces and kept pace with the Swiss until the final downhill section when Schurter pulled away.
Van der Poel held off Henrique Avancini, who became the first Brazilian to record a World Cup XCO podium, with Switzerland's Florian Vogel trailing in fifth.
Schurter, 32, revealed: "I knew from the previous year that the finish is really short and super bumpy, so my goal was to try and get a little gap in the downhill and go all out. I would say I am in awesome shape and I am super happy about my form."
Kerschbaumer, 26, said: "Today I am really happy with second place. All the fans stayed with me today. Last year I had a crash here, so this year was really good."
1. Maja Włoszczowska POL 1:30.51
2. Emily Batty CAN +0.09
3. Jolanda Neff SUI +0.30
4. Pauline Ferrand-Prévot FRA +0.38
5. Gunn-Rita Dahle Flesjå NOR +0.41
UCI Mountain Bike World Cup women's XCO standings after four out of seven races:
1. Jolanda Neff SUI 975 points
2. Annika Langvad DEN 923
3. Pauline Ferrand-Prévot FRA 806
4. Maja Włoszczowska POL 732
5. Anne Tauber NED 715
Val di Sole men's cross-country result:
1. Nino Schurter SUI 1:26.32
2. Gerhard Kerschbaumer ITA +0.06
3. Mathieu van der Poel NED +1.09
4. Henrique Avancini BRA +1.14
5. Florian Vogel SUI + 1.32
UCI Mountain Bike World Cup men's XCO standings after four out of seven races:
1. Nino Schurter SUI 1130 points
2. Mathieu van der Poel NED 820
3. Maxime Marotte FRA 711
4. Florian Vogel SUI 617
5. Henrique Avancini BRA 586