Well Scripture refutes your position.Not "He who believes is saved then should be baptised".
ACTS 16: BELIEVING PRECEDES WATER BAPTISM
25 And at midnight Paul and Silas prayed, and sang praises unto God: and the prisoners heard them.
26 And suddenly there was a great earthquake, so that the foundations of the prison were shaken: and immediately all the doors were opened, and every one's bands were loosed.
27 And the keeper of the prison awaking out of his sleep, and seeing the prison doors open, he drew out his sword, and would have killed himself, supposing that the prisoners had been fled.
28 But Paul cried with a loud voice, saying, Do thyself no harm: for we are all here.
29 Then he called for a light, and sprang in, and came trembling, and fell down before Paul and Silas,
30 And brought them out, and said, Sirs, what must I do to be saved?
31 And they said, Believe on the Lord Jesus Christ, and thou shalt be saved, and thy house. [Note: no mention of baptism]
32 And they spake unto him the Word of the Lord, and to all that were in his house. [Note: the Word of the Lord = the Gospel]
33 And he took them the same hour of the night, and washed their stripes; and was baptized, he and all his, straightway.
34 And when he had brought them into his house, he set meat before them, and rejoiced, believing in God with all his house.
This follows the same sequence as all the other incidents in the book of Acts: (1) the Gospel is preached, (2) sinners believe on Christ and are saved, and (3) they are then baptized and go on their way rejoicing.