Three points should be considered before moving onto the main answer:
1-Satan pretended to be benevolet and friendly when he tempted Adam. Therefore, it should not be assumed that the temptations of Satan, though powerful, will deprive man of  volition (free will). However, man can stand against it through the power of wisdom and faith. In other words, Satan's temptations do not compel  man to commit a wrong . In fact, free will still remains, although resisting the temptations of Satan requires more steadfastness and resistance, and even the toleration of pain and suffering. Anyways, such temptations do not relieve any one of  responsibility, as it did not relieve Adam of any responsibility. So we can see that notwithstanding the  causes of disobedience created by Satan to encourage Adam to disobey God,  God still considers Adam responsible for his act.¹  
2-According to the Shia, no prophet commits any sins and we know that Adam was one of the divine prophets. Therefore what has been mentioned in the Quran about the prophets and their sins  relate  to the "relative disobedience" and "the abandoning of more meritorious acts”, and not "absolute sins". 
An absolute sin is the same as violating prescriptive prohibitions and the violation of God's absolute order that includes any type of leaving an obligatory duty and Haram (unlawful) acts. However, relative sin is a non Haram act done by a great man who is not deserving to do such an act considering his position and status. Some times, a Mobah or even Mostahab act is not befitting of divine personalities. In this case, doing such an act is considered as a "relative sin". For example if a faithful and rich man gives little help to save a poor person from poverty then undoubtedly this help, even being very negligible, is not Haram rather it is Mostahab. But anyone who hears it may blame the act as if he has committed a sin. Because it is expected that such a faithful and rich man would do something greater than what he has done.
Similarly, acts of divinely inspired individuals will be measured according to their superior position. Sometimes it is comparatively called sin or "Dhanb" (sin).For example, a prayer that may be an excellent prayer for a normal person will be considered as a sin for the Walis of Allah because the Walis of Allah are not expected to have a moment of negligence during worshiping rather they should be immersed in God's glory and beauty during worshiping according to their knowledge, piety and position. It is also true about their other acts besides worship and their acts will be measured according to their position .Therefore if they do an act which is the lesser of two good actions, the will be blamed by God.²
Therefore Adam's prohibition of the "forbidden tree" was not a full out prohibition rather it was an ‘abandoning of the better action’. But this act done by Adam (a) was considered as an important act due to Adam's (a) position and his act (though it was Nahy Kerahati) led to such a severe punishment by God. However it is possible to say that Adam's (a) prohibition of the "forbidden tree" had been" Irshadi" not "Mowlavi".
To further explain, sometimes God prohibits something since He is the owner of the man, has authority over him and is his Lord. So it is necessary for each man to obey God's commands.This kind of prohibition is called "mowlavi prohibition". But sometimes God forbids man from doing something just to say that doing this act will have adverse effects on him. For example just like when a doctor prohibits his patients from eating harmful foodstuffs. Undoubtedly, if a patient acts against the doctor's prescription, then it will not be considered as insult or violation of the doctor's advice. But actually the patient has ignored the doctor's guidance or advice and put himself into trouble. Also in the case of Adam's (a) story, God had told him that eating the forbidden tree's fruit would cause his expulsion from heaven and it would put him in trouble. It is guidance (Irshad) based command not a  prescriptive command. Therefore Adam (a) just disobeyed the Irshadi prohibition and there was no real sin.³
3. Moreover, Satan in other verses attributed his sin and oppression to the human and disclaimed any kind of responsibility. Satan considered himself entirely impartial.⁴ Satan, addressing people on the Day of Judgment, says: God promised you the right and I promised you the wrong. I did not keep my promise but did not force you to do the wrong one. It was you who accepted my invitation by your free will. So do not blame me but blame yourself.⁵ 
God in another verse says:" certainly you will not dominate my servants unless they follow you voluntary.⁶
Conclusion: Through careful attention to what was mentioned, it can be said that undoubtedly God's power is more than Satan's power. Because Satan is God's creature and the creature's power is not more than that of the Creator. So if you observed that Adam (a) used the forbidden tree, it was not because of Satan's verbal influence; rather, it was due to Satan's temptations which were successful. But as mentioned before, it was just an ‘abandoning of the greater act (lapse)’. Also, in the Day of Judgment, humans will be deserving of punishment because of their disobedience by their own free will. Therefore, we should not try to compare the power of influence in the word of God or Satan; rather we should know that God's power is greater than any other power. But it is human beings who do not act according to their own free will.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

1-Makarem Shirazi,Naser, Tafsir Nemoneh,V6,P120,Dar al Kotob al Islamieh,1995.
2- Abandoning the Priority (lapse) means that human leaves the better act and does what it is good or Mobah.
3-Tafsir Nemoneh,V6,Pages123,124,125.
4-Tabatabayi, Mohummed Hussein,Tafsir al Nemoneh,Translated by Moosavi Hamedani,V8,P48,Published by Jameeh Modarresin,Ghom 1995.
5-Ibrahim Surah,22.
6-Hijr Surah,24.