No, Krishna was not incompetent against Jarasandha. In fact, Krishna and his army has defeated Jarasandha and his army eighteen times.
Krishna running away from Jarasandha implies that, Jarasandha was destined to be killed by Bhima in duet.
Realising that jarAsaMdha was skilled in mace fight, valiant balarAma became angry. He abandoned the mace and picked up his best club.
Seeing the angry balarAma picking up the infallible club, terrible at sight, in the great battle,
the voice of the witness of the world, was heard in the sky, telling baladeva (balarAma), who had picked up his weapon, the club.
O rAma (balarAma)! mAgadha (jarAsaMdha) is not to be killed by you. You need not lament. I have foreseen his death. Hence control yourself.
In a short time, the lord of magadha (jarAsaMdha) will lose his life.
Hearing this, jarAsaMdha became disappointed as if he lost his mind. balarAma, having club as his weapon, did not strike jarAsaMdha again.
Both stopped fighting. The vR^iShNi-s and the kings also stopped fighting. In this way the terrible battle between them became devoid of any interest.
(vaishampAyana said) O great king (janamejaya)! (In this way, the terrible battle that resulted in ) killing each other for a long time came to an end.
When jarAsaMdha was defeated, he left the battlefield. As the sun set, the yAdava-s did not chase him in the night.
Assembling their forces, the (yAdava-s) warriors of great power, protected by keshava (kR^iShNa), achieving their aim, happily entered the city.
king jarAsaMdha, disappointed, returned to his city. The kings who followed him also returned to their kingdoms.
O tiger of the kuru race (janamejaya)! Even though they defeated jarAsaMdha, the vR^iShNI-s did not think so. The king jarAsaMdha is most powerful.
The yAdava-s fought with jarAsaMdha ten and eight (eighteen) battles. The powerful yAdava-s were unable to kill him.
O One with great intellect (janamejaya)! king jarAsaMdha has twenty akShauhiNi-s who came for fighting the battle for him.
O the bull of bharata race! Compared to jarAsaMdha's army, the army of vR^iShNi-s is meager. O the king of kings (janamejaya)! they were baffled on being attacked by jarAsaMdha along with other kings.
jarAsaMdha again came prepared and attacked yAdavas, protected by kR^iShNa.
After defeating jarAsaMdha, the king of magadha in the battle, the lions of the vR^iShNi race, the great chariot fighters lived comfortably.