Sarach Yuyen joined Muangthong United in the 2010 season, and at that time, he was 17 years old. Later, Muangthong sent him to Phuket FC on loan for a year in 2010. He was an important power in Phuket FC, and led the team to grab the championship for Division 2 League, south region.
In 2011, Sarach was still an important strength for Phuket FC when they were promoted to Division 1 competition.
In 2012, Slaviša Jokanović, the head coach of Muangthong United, included Sarach in the first team roster, and then Yooyen played his first Thai Premiere League match soon after. In this match, Muangthong United defeated Singtarua FC (now Thai Port) 5-1 on March 25. In that game, Sarach Yooyen was subbed in during the second half and was the man who scored and moved Muangthong to a 4-1 lead. It is also counted, therefore, as the first game and first goal for Muangthong United.
Sarach have revealed his feelings about that match,
“I have not forgotten the day that I signed the contract with Muangthong. Even though I was sent to play in Phuket FC on loan, due to how I was still 17 years old, I have always told myself that I have to prove myself and climb up to play in the big team with Muangthong. I dreamed to play alongside with many of my idols such as Teerasil Dangda and Datsakorn Thonglao. When 2012 came and I was invited to play on the big team, I was very happy. Then the first time on pitch came faster than I expected, because it was only on the 2nd match of the season, and Slaviša Jokanovićsubbed me in to play in the match against Singtarua FC. At that time we were leading 3-1, and the head coach told me that he let me enter because we were leading in the game and told me to find a good space in the field. He also told me not to be nervous and just be myself, as well as telling me that I was able to score, which I really was able to! I was very happy to have been able to enter my first match with the big team and to score in my first match. I really cannot forget.”