Fourteen teams contested the 1965–66 Nationalliga A. Basel finished the season in sixth position with 27 points.
After playing seven test games Benthaus made his Swiss League debut on 22 August 1965 at the Landhof in the home match against FC UGS Genève.
Basel played an away match in the Stadio Cornaredo against FC Lugano in the semi-final which ended goalless and therefore a replay was required.
The replay was played in the St. Jakob Stadium and goals from Karl Odermatt and Benthaus himself gave Basel a 2–1 victory to qualify for the final which was to take place three days later.
After 88 minutes of play, with the score at 1–1, referee Karl Göppel awarded Basel a controversial penalty.
Subsequent to the 2–1 for Basel the Lausanne players refused to resume the game and they sat down demonstratively on the pitch.
Although they were within reach of the table top the entire campaign, they messed everything up towards the end of the season as they lost five games out of seven.
Basel won 13 of the league 26 games, drawing five, losing eight times, and they scored 49 goals conceding 33.
In the Swiss Cup Basel started in the round of 32 with a home match against lower classed FC Le Locle, but the game had to go into overtime.
After Le Locle took the lead just after half time break, Frigerio netted the equaliser shortly before the end.
In the next round Basel played an away game against FC Zürich and were defeated 1–0 and the campaign was ended.
Basel won 13 of the 26 games, drawing ten, losing three times, they scored 48 goals conceding 28.
In the 1968 Cup of the Alps the team managed to win the group and played in the final against FC Schalke 04 but were defeated 3–1 after extra time.
In the quarter-final, played in November, Basel had a two legged tie against Xamax-Sports NE (later renamed Neuchâtel Xamax).
The first leg, which played on 17 September 1969 in the St. Jakob Stadium in front of 37,587 spectators, ended in a goalless draw.
In the 1969 Cup of the Alps Basel won their group and in the final they beat Bologna 3–1 after extra time.
Towards the end of his playing career Benthaus stood on the side line as team manager and he only substituted himself into the game if it was not running as he wanted it.
Benthaus played 11 games in the 1970–71 FC Basel season, just four of which in the starting formation and seven as an inwards substitution.
In the second leg played in the St. Jakob Stadium Basel won 2–1, the goals being scored by Urs Siegenthaler und Walter Balmer.
The second leg at home also ended with a defeat, 2–1, despite the fact that Odermatt put Basel one up with a penalty after 36 minutes.
This being the second last home match of the season on 27 May against Luzern[14] Basel won 18 league games, drew 7 and only suffered one defeat.
In the Swiss Cup Basel advanced to the final, which was played on 22 May 1972 in the Wankdorf Stadium but they were defeated 1–0 by Zürich through a goal by Daniel Jeandupeux in extra time.
Benthaus coached the team to beat Servette 8–0, Lausanne Sports 2–1 aet and Sion 6–1 to reach the final.
This was won by Basel who defeated FC Winterthur 4–1 in the final which took place on 11 November 1972 at the Letzigrund in Zürich.
In the Swiss Cup Basel reached the final, which was played on 23 April 1973 in the Wankdorf Stadium against Zürich.
In extra time Peter Marti (92) and Fritz Künzli (101) scored the goals to give Zürich the title for the second consecutive year in a final against Basel.
In the 1973–74 season Basel finished the championship in fifth position, in the Swiss Cup they reached the quarter-finals.
They ended the championship ranked sixth with just nine victories, ten drawn games and seven defeats.
In their 30 league games Basel won eleven, drew six and lost thirteen matches, which meant that the totaled 28 points, scoring 47 goals and conceding 51.
He coached Basel's legendary team of the late 1960s and the 70s that won the Championship title six times (five of which in seven years) as well as the Cup in 1967 and 1975.